Cargo lamps w Reverse and fog-lights w parking lights wiring help

[Daryl Casey]

2020 Sierra 1500 SLT

After searching and reading through many threads without the specific answers I'm looking for, I'm hoping for some information and advice.

 

I'd like to have

1 )the fog-lights come on with the parking lights, so the fog-lights are on all the time (even staying on with high beams if possible)

2) the Cargo Lamps illuminate when the truck is in Reverse.

 

I'd like to know what plug/pin number to jump with the diode and what size diode/direction the diode goes (which way the stripe faces). Bonus points for photos (see below)

 

I found this photo in a 2014 - 2018 GMC thread. The thread said the brown to pink is the cargo-reverse light mod and the brown to brown was the parking lights-fog lights mod.

 

Are the plugs/wires/diode direction the same for the 2020?

Is the 1Amp D1 diode the right one for these mods? Is the diode just pushed into the back of the plug, alongside the wire?

 

I'd appreciate any help that can be provided. Please be sure to dumb it down for me and any other future searchers. I know I need all the help I can get!!

 

Thank you for your time,

DC

 

 

 

[kodiakdenali]

Replied to the other thread, saw it in the popular topics list and thought I could help, didn't even notice it was in the wrong forum. copying here:

 

 

Disclaimer:  This is based off the upfitter manual schematics and technical data, It would be best to look up and confirm and verify this information before you make modifications!

To activate the Fog lights with the parking lights you can use a diode to jumper the relay controls:

fog lights relay controls is X5 (brown? connector) pin 10, BRN/WHT wire

Parking lights relay control is X5 (brown? connector) pin 22, BLU wire

both are ground triggers for relays so to activate fog lights with parking lights:

diode jumper Parking Lights Relay Control BCM X5, pin 22, BLU wire (GND signal) to Fog Lights Relay Control BCM X5, pin 10, BRN/WHT wire (GND signal), diode stripe goes towards Parking Lights, BLUE wire

refer to the upfitter manual, pages (these are from the 2020 sierra book, pages may vary some with other years or for the silverado manual)

7-255 for BCM connector X5 pinout

2-24 for fog lights control schematics

2-28 for parking lights schematics, as an example. the parking lights are actually on a number of different schematics. , 2-31, 2-32. 2-33 etc.

 

for cargo lights on with reverse lights,

backup lights relay control is X5 pin 26 BLU/BRN wire, note, this is a +12V relay control wire, not ground like usual. This relay is labeled the trailer backup lights relay in the schematic. according to the schematic, it is responsible for sending the reverse lights command to the tail light assemblies (for sierra LED tail lights, others may be different)

cargo lights (standing lamp relay control) is BCM X6 (pink) connector, pin 26, BRN/WHT and this also is a +12V signal.

so for cargo lights on with reverse lights

diode jumper backup lights relay control, BCM X5, pin 26 BLU/BRN  (+12V signal)  to cargo lights relay control BCM X6, pin 10, BRN/WHT (+12V signal), the diode strip goes towards the cargo lights, BRN/WHT wire

note that because of the two different circuits for the cargo lights, this should activate the cargo light on the back of the cab and the "hitch" light on the back of the tailgate, but will not turn on the interior bed lights.

references:

7-256 BCM X6 pinout (cargo lights)

7-255 for BCM X5 pinout (reverse lights)

2-31, 2-32 for backup lights schematics

2-38 for cargo lights schematics

 

in both cases the only extra load we are adding to the source signal is a relay control, very low current draw. any standard diode will be fine.

 

If anyone sees any errors, please let me know!

Edited January 5, 2021 by kodiakdenali
somehow mixed up the pin numbers, but the wire colors were correct. fixed the error.

[Daryl Casey]

@kodiakdenali Thank you very much for the information! 

 

Ill be getting my 1 Amp diodes from Amazon, what voltage number should I be looking for or does it matter? I've seen 20V to 400V.

 

My apologies for the noob questions, I just want to make sure I'm doing this correctly and using the proper materials.

 

Thanks again,

DC

[kodiakdenali]

30 minutes ago, Daryl Casey said:

@kodiakdenali Thank you very much for the information! 

 

Ill be getting my 1 Amp diodes from Amazon, what voltage number should I be looking for or does it matter? I've seen 20V to 400V.

 

My apologies for the noob questions, I just want to make sure I'm doing this correctly and using the proper materials.

 

Thanks again,

DC

I'd just get whichever of the two is cheaper!

with diodes there are 2 different voltages that are important when picking one out, the forward voltage is a voltage drop across the diode. you don't get that "one way valve" for free, you lose some voltage, usually 0.6-0.7V, no where near enough to cause a problem here, the voltage will still be plenty high to activate the relay.

the other concern is the reverse voltage (this is probably the spec that you are looking at), a diode is a device which prevents the flow of current in one direction should there be a reverse biased voltage that it has to "hold back," how much voltage can it handle before possibly failing? This is a 12V circuit, even with the alternator in operation you're looking at 14-15V at most, so either of those should be just fine for the application.

[Daryl Casey]

34 minutes ago, kodiakdenali said:

I'd just get whichever of the two is cheaper!

with diodes there are 2 different voltages that are important when picking one out, the forward voltage is a voltage drop across the diode. you don't get that "one way valve" for free, you lose some voltage, usually 0.6-0.7V, no where near enough to cause a problem here, the voltage will still be plenty high to activate the relay.

the other concern is the reverse voltage (this is probably the spec that you are looking at), a diode is a device which prevents the flow of current in one direction should there be a reverse biased voltage that it has to "hold back," how much voltage can it handle before possibly failing? This is a 12V circuit, even with the alternator in operation you're looking at 14-15V at most, so either of those should be just fine for the application.

@kodiakdenali Thanks again for the help and for dumbing it down for me. I just ordered the diodes so once they arrive I'll be doing this mod.

 

As for installing the diodes, it looks like you just insert the diode into the back  of the BCM plug. Any other advice or tips for installing the diodes?

 

[kodiakdenali]

56 minutes ago, Daryl Casey said:

@kodiakdenali Thanks again for the help and for dumbing it down for me. I just ordered the diodes so once they arrive I'll be doing this mod.

 

As for installing the diodes, it looks like you just insert the diode into the back  of the BCM plug. Any other advice or tips for installing the diodes?

 

well, you may not like my advice

I see a lot of posts where the diode was just inserted into the connector and press fit against the pin. I would not do it that way, but doing it "right" requires some skills and tools. I would highly suggest soldering a short lead of wire onto the diode pins, heat shrink it, and splice that into the bcm wires either by soldering it in or using taps, which should be ok for an interior circuit (inside the cabin, reasonably free from moisture).

why? that press fit is unreliable. you could end up with a poor connection. over time and bumps it could loosen up, you could end up with intermittent connectivity, the cargo lights flashing etc. the worst case though is pulling current through a poor connection, something that would be very hard to detect in this case...until it burns your truck to the ground. ok, we're talking about relay controls here, they are pretty low current. if you were trying to jumper some of the BCM circuits that directly drive lights and you're running a larger diode with a couple amps I'd tell you don't even think about doing it that way, you're just asking for a fire. with relay control you're passing milliamps through the diode, however a poor connection is still dangerous.

now, it seems that tons of people have done this mod by just shoving the diode leads down the connector cavities and haven't had a problem, so you'd probably be just fine. but I wouldn't do it that way on my truck.

completely up to you, stressing again this seems to be the go-to way of doing this and it seems to work safely. but just saying, if that relay draws 100mA on the coil, and you have a bad connection with the pin (which could even develop a couple years down the road should the diode leads get some surface corrosion on them or work their way loose over rough roads) that 100mA would be enough current to generate enough heat to char or melt the BCM connector or even start a fire. I'm an ECE (electrical/computer engineer) so I like to do this kind of thing the right way. I don't change vehicles very often so when I do a mod like this I do it so it will work safely and reliably for 200k miles and 10 or more years.

Even if you are just pulling dozens of mA though a very poor connection, the leads can get hot enough to burn your fingers in a matter of seconds. Neither the diode nor the connector/pins on the BCM harness are designed for making electrical connections that way. At least on my projects, it's not a risk that I take.

 

Not to mention, especially with the reverse lights/cargo lights mod, there is a long diode lead completely exposed, not insulated, and spanning across 2 connections in the picture in the first post. This could short against something and either cause mod failure, bizarre behavior (wrong lights coming on), or damage the BCM or its wiring. That is definitely not a good idea. At very very least, put some heat shrink or electrical tape over the exposed parts of the leads.

Edited December 16, 2020 by kodiakdenali

[Daryl Casey]

@kodiakdenali

I believe I'll take your advice and fix my diodes up just like you recommend. Better to do it right the first time. I plan on keeping this truck for a very long time so I might as well make the mods bombproof. I'm hesitant about cutting the wires (truck is only 4 months old!) to solder in the diode, so I'll use taps to connect the diode into the wires. Using the taps will let me connect the diode in a place along the wires to keep it out of the way.

Once I get the diodes in I'll post up some pics of how they look after I solder the leads and heat shrink them. 

I can't thank you enough for your advice. If you have any other good electrical mods up your sleeve, I'd appreciate you sharing them with me!

 

 

[kodiakdenali]

23 minutes ago, Daryl Casey said:

@kodiakdenali

I believe I'll take your advice and fix my diodes up just like you recommend. Better to do it right the first time. I plan on keeping this truck for a very long time so I might as well make the mods bombproof. I'm hesitant about cutting the wires (truck is only 4 months old!) to solder in the diode, so I'll use taps to connect the diode into the wires. Using the taps will let me connect the diode in a place along the wires to keep it out of the way.

Once I get the diodes in I'll post up some pics of how they look after I solder the leads and heat shrink them. 

I can't thank you enough for your advice. If you have any other good electrical mods up your sleeve, I'd appreciate you sharing them with me!

 

 

You're welcome and good luck! I look forward to seeing how your mod comes out!

I do have a whole list of similar things I'm going to do, I need to remind myself to only work on one project at a time, I've got a couple of other things on my list first. but yep, lots of fun stuff coming!

[aragrev7]

You're welcome and good luck! I look forward to seeing how your mod comes out!
I do have a whole list of similar things I'm going to do, I need to remind myself to only work on one project at a time, I've got a couple of other things on my list first. but yep, lots of fun stuff coming!

Very useful info. I might tinker around soon.
I wonder what other mods like this you are thinking? I’m interested! I did a lot of these on my Acura back when.
One thing I miss is the tailgater switch. Any idea of how to get the reverse lights and/or cargo lamp on while driving? I used to use this with my lowered Acura for people that tailgated. Had mega bright LED reverse bulbs in and they would back right off when I did it. Especially the lifted trucks trying to be cute. [emoji4]


Sent from my iPhone using Tapatalk Pro

[kodiakdenali]

35 minutes ago, aragrev7 said:

 

Very useful info. I might tinker around soon.
I wonder what other mods like this you are thinking? I’m interested! I did a lot of these on my Acura back when.
One thing I miss is the tailgater switch. Any idea of how to get the reverse lights and/or cargo lamp on while driving? I used to use this with my lowered Acura for people that tailgated. Had mega bright LED reverse bulbs in and they would back right off when I did it. Especially the lifted trucks trying to be cute.


Sent from my iPhone using Tapatalk Pro

 

ha.

as far as I know the cargo lights can be activated with the dash switch even while driving. they probably aren't bright enough to deter a tailgater though.

you could activate the reverse lights with a momentary pushbutton switch to connect 12V to the backup lights relay control:

backup lights relay control, BCM X5, pin 26 BLU/BRN  (+12V signal) 

that should turn them on, probably not legal to have backup lights on while driving forwards...but then neither is tailgating!

 

I'll have to think about detailing some other projects. I have some plans for some forward and rearward lighting enhancements. I need to boost up the backup lights with some aux units. this is mostly because I have to back into my garage to make this truck fit and the stock lights just aren't good enough for me. plus the backup camera can certainly do with more light, it gets really noisy and goes to a low frame rate to compensate for low light conditions...why not fix the low light condition rather than compensating for it with the camera!

 

then I'm planning to do a bunch of BCM mods just like what you're working on, but I have a whole list of them that I want to do. I'm going to do it all at once with a custom PCB and make each mod individually switchable so can enable/disable them at any time.

 

If I'm so inclined I might alter the autolights as well. I did this on my old truck and really liked the results, I didn't like the way autolights worked. for one thing they would not turn on or stay off when I wanted them to, and I didn't like that factory autolights are all on or all off and nothing in between. I built a controller with light sensing and tied into all the lighting systems. disabled the factory autolights and implemented my own logic which would progressively turn on the lights one system at a time as it got darker or back off again one system at a time as it got lighter. Parking lights then fog lights, then headlights as needed. hooked it up with an LCD screen which would display the lights status and tell me what light level it saw so I could keep track of that it was doing. It was really fun to watch it work, finally an automatic lighting system that always seemed to have the lights on exactly the way I wanted them when I wanted them.

building electronics can be addictive

[Daryl Casey]

@kodiakdenali

One light mod you might give some thought to is how to make the task lights (the lights on the mirror) come on when the headlights come on, or get the task lights to come on when the truck is in park. They come on when the button on the headlight control is pressed, but the button needs to be pressed each time for the lights to come on. I'm not sure what the purpose is of those lights.

Like you, I'm looking for more light when the truck is in reverse. I saw a mod where small LED lights were placed in the footwells of the rear bumper. They were flush mounted so the footwells were still usable. I've also looked at the light bars that go under the tailgate. They seem to provide extra lighting as well. 

I look forward to hearing about other light mods you do. Please post them up here so we can learn!

 

 

[kodiakdenali]

8 minutes ago, Daryl Casey said:

@kodiakdenali

One light mod you might give some thought to is how to make the task lights (the lights on the mirror) come on when the headlights come on, or get the task lights to come on when the truck is in park. They come on when the button on the headlight control is pressed, but the button needs to be pressed each time for the lights to come on. I'm not sure what the purpose is of those lights.

Like you, I'm looking for more light when the truck is in reverse. I saw a mod where small LED lights were placed in the footwells of the rear bumper. They were flush mounted so the footwells were still usable. I've also looked at the light bars that go under the tailgate. They seem to provide extra lighting as well. 

I look forward to hearing about other light mods you do. Please post them up here so we can learn!

 

 

I do want to implement fog lights on with low beam headlights (which would cover the high beams as well) but task lights with low beams I don't think its a good idea, they're too much of a flood light effect, it would be blinding to other drivers. although, Task lights on with high beams is one of the items on my list. It would look neat, and give you extra peripheral vision, and there's no worry about blinding other drivers because you can't use high beams in a situation where you'd be blinding them anyway.

I also think the task lights on this truck are kind of stupid. never mind that that button in the headlights dial should be the button for the fog lights and not for these task lights! Those two buttons should swap places...but regardless. the task lights as they are right now are mostly useless. when I thought to the concept of task lights, I was thinking total perimeter illumination so you can see anything and everything you're doing if you ever had a flat or other roadside emergency, needed to do a repair in the dark or anything else. such lighting would also come in very very handy when parking in tight locations like parking lots or the garage. this truck has cameras all over it to help with those tight maneuvers...but not enough light where the cameras are pointed! for me the #1 best use for the stock task lights would be for very low speed tight maneuvering in dark situations...but of course those lights cannot be used in that case. GM should have at least set them up so they can be used in drive or reverse at speeds < 10mph or something. then at least they'd be useful for parking. I intend to fix all of that!

I actually was impressed to see that one pic of the guy who put light pods into the corner steps...because that's exactly what I was planning to do. we both had the same idea. I never did like those corner steps, I think they're kind of ugly. and with the multi-pro why would I ever need the corner steps? the only time the multipro can't be used to get into the bed is when I have a trailer attached...and in that case I just step on the trailer! but I decided I didn't completely hate them since they are a perfect place to add lights. I plan to add flood lights just like that other owner (I've got them on hand and my replacement set of step pockets for modification is scheduled to be here today) I'm planning to add an extra rear marker light in there as well because I want some extra lighting but I'm not really sold on the look of the tailgate bars. also considering a white flood light in there attached to the bed lights circuit. not that I will ever use the corner steps, but just to compliment the look with the step lighting I've already got on the multi-pro (GMC accessory).

the rear lights I got were cheapies, we'll see how they hold up. but they are triple beam, spot lights for distance, flood lights for fill, and its got an extra set of LEDs on the sides for a very wide pattern. hopefully they will be good enough, if not I'll add yet another light, something like a rock light, in there aimed sideways. this extra light is going to help a lot for garage maneuvers.

[Daryl Casey]

@kodiakdenali

I agree 100% with you on the placement of the task light/fog light switch. Are the task lights on a separate circuit? I'd like for them to come on when the truck is remote started and after the truck is turned off similar to the puddle lights. Maybe puddle lights to task lights w a diode?

 

As for the step pocket LEDs, I was looking at a flush mounted set on Amazon. Any recommendations on which ones to use? The lights power wire would tap into the trucks reverse light wire and the ground would go to the chassis or would it have to go into a ground wire?

 

The tailgate light bar I was researching plugged into a harness made by Putco. The Putco harness connects into the trucks wiring harness so it doesn't require any tapping or soldering. Then the light bar connects into the Putco harness. Like you, I'm all for maximum lighting when the truck is in reverse. Not only for my benefit but hopefully for other drivers or pedestrians.

 

 

[kodiakdenali]

1 minute ago, Daryl Casey said:

@kodiakdenali

I agree 100% with you on the placement of the task light/fog light switch. Are the task lights on a separate circuit? I'd like for them to come on when the truck is remote started and after the truck is turned off similar to the puddle lights. Maybe puddle lights to task lights w a diode?

 

As for the step pocket LEDs, I was looking at a flush mounted set on Amazon. Any recommendations on which ones to use? The lights power wire would tap into the trucks reverse light wire and the ground would go to the chassis or would it have to go into a ground wire?

 

The tailgate light bar I was researching plugged into a harness made by Putco. The Putco harness connects into the trucks wiring harness so it doesn't require any tapping or soldering. Then the light bar connects into the Putco harness. Like you, I'm all for maximum lighting when the truck is in reverse. Not only for my benefit but hopefully for other drivers or pedestrians.

 

 

I would need to review the schematics some more, but I think the task lights are a discrete signal to the bcm that gets ground whenever the button is pressed. the fog lights switch unfortunately is not, its a resistor ladder. so it and a few other controls (dimmer and cargo lights buttons I think) are all on the same circuit, and the BCM detects when those buttons are pressed by a difference in resistance on that wire. so its not impossible to reuse those buttons, but probably not worth it.

sneak peek at what I was planning as the ultimate goal, which will be a while before I finish it all, I actually want to take over the task lights switch and run it to my own logic, disconnect it from the BCM and implement a different means of activating the task lights, maybe something like an upfitter switch? the BCM's control of the task lights is way too restrictive. like I mentioned, I want them to be able to come on in gear at least at low speeds for tight parking lot maneuvers and such, its probably easier just to take those lights completely out of BCM control.

I want to add 2 sets of fog lights to the front of my truck, one set LED cool white with its goal being visibility of me, corner/ditch visibility to the driver, and looks. then I want to try to add a completely separate set of LED fog lights which are the amber colored lights, which of course are vastly more effective for poor weather. fog, rain etc. I think I will use the factory task lights button (its icon looks enough like fog lights to me!) to activate the white fog lights as the "primary" fog lights, because it just makes way more sense for the fog lights control to be on the same dial as the rest of the headlight controls. then I'll power the amber fog lights off the stock fog lights circuit and so the factory for lights button will basically operate my bad weather fog lights. It will take a while to get it all set up, but I think it will be pretty cool when done.

 

as for the task lights. actually, that on my list already. the puddle lights come on as the courtesy lights after you turn the truck off, and as approach lights when you hit the unlock button. I don't think they come on in any other situation. in those cases the headlights, fog lights, and backup lights all come on as well (I think). in all of those situations I think it would be neat to have the task lights activate and also the cargo lights.

the task lights though you will need a relay to do it safely. there is no stock relay control, the BCM directly provides the 12V that run the LEDs. in fact to do it the best way you'll need 2 relays. you can control them with the same inputs, but that will keep both task lights separated so you still have the stock functionality of being able to turn on just the left or right or both  at once. (you could also do this with a single relay and diode isolate the outputs, this is how boost auto's kit does it, but I think 2 separate relays gives me more flexibility for other things I want to do). Both the puddle lights and task lights are driven directly from the BCM, but I wouldn't recommend jumpering them with a diode directly. you would be adding a significant load to the source circuit beyond what its designed for and could cause problems. a relay is safer.

actually, I kind of want to tie both of those functions together bi-directionally..as in any time I turn on the task lights, I'd like the puddle lights on as well. any time the puddle lights are on, I think the task lights should be on. I'll design my stuff so all of this is easily switchable, but I see a good use for both situations. the puddle lights would certainly be useful in tight quarters when using the cameras under the mirrors to watch how close my front/rear wheels are getting to an obstacle.

[kodiakdenali]

25 minutes ago, Daryl Casey said:

@kodiakdenali

I agree 100% with you on the placement of the task light/fog light switch. Are the task lights on a separate circuit? I'd like for them to come on when the truck is remote started and after the truck is turned off similar to the puddle lights. Maybe puddle lights to task lights w a diode?

 

As for the step pocket LEDs, I was looking at a flush mounted set on Amazon. Any recommendations on which ones to use? The lights power wire would tap into the trucks reverse light wire and the ground would go to the chassis or would it have to go into a ground wire?

 

The tailgate light bar I was researching plugged into a harness made by Putco. The Putco harness connects into the trucks wiring harness so it doesn't require any tapping or soldering. Then the light bar connects into the Putco harness. Like you, I'm all for maximum lighting when the truck is in reverse. Not only for my benefit but hopefully for other drivers or pedestrians.

 

 

I would have to look up what I picked...I got the ones I'm going to use on amazon. they are cheepies, but my mod budget is running thin if they last me a year then fail oh well, I'll put in a better brand next. but I think for reverse lights and approach etc they are probably fine. the ones I picked were 4" off road lights, the rear of the pod is rounded which actually fits pretty darn well with the curved shape of the front wall of the step pocket. I haven't decided if I'm just going to  fit them right in there or cut an opening and try to make them look more flush mounted. I am still waiting on my replacement pockets to assess the situation.

as for how to wire them up, I bought 2 aftermarket harnesses. the putco one which attaches to the factory tail light circuits and a curt product which plugs in line with the 7 pin trailer harness. it was pretty affordable, its designed for adding a 4 pin trailer connector in line with the 7 pin while leaving the 7 pin available. I bought it for the factory matched connectors, I will use that to access a good, high current, source of 12V power. I'll need it for other mods in the future (probably months, but eventually my bed and multi-pro step lights will come on automatically when I lower the gate) I also don't need all of the signals of the putco harness, so I'm going to cut up both of them and build the harness that I need. I am probably going to use a relay triggered by the putco backup lights wire to power the add-on flood lights using the 30A 12V power from the trailer harness. You can't use the trailer light signals directly as it tends to trigger trailer detection by the truck and puts everything into trailer mode which I don't want. I'm not sure if the stock backup lights circuit will handle the extra load. or the putco harness itself, which is designed for connecting a light bar, not off road pods. but just like you all of this will end up being plug and play, no permanent modification to the stock wiring.