Foglights On With High Beams

Eddie 70 · November 12, 2015

Just found a couple of 4003 diodes in the box with my Fluke left over from some other projects. I know where to put these to good use. Looks like I will have fogs on with high beams and cargo on with backup.

irish4life8911 · November 15, 2015

My '15 Sierra All Terrain had different color wires in box 10 to 18. Box 10 was brown/ purple and jumped to box 18 which was All Brown wire.

But the box diagram is still correct!

Thank you spurshot!

CptMcSaug · November 21, 2015

Just did mine, box diagram was right but the wire colors were different. Maybe they changed them in 15? I can't recall the colors but I'm 90% sure 18 was Brown/Purple and 10 was all Brown.

But I tested it out by placing a towel over the sensor. All worked correctly and the truck didn't spark or burn to the ground yet

Also added some air to the tires man was it needed.

eznonby · November 25, 2015

Has anyone found an alternative to this mod for a '15 Silverado? After trying and trying I've had no luck getting this to work.

ClemsonFan · December 4, 2015

Big thanks to Wurgs for the diodes. Looking forward to completing this mod soon.

No Tyme · December 4, 2015

Has anyone found an alternative to this mod for a '15 Silverado? After trying and trying I've had no luck getting this to work.

I understand how you got to where you are. Took me three separate times and the third diode to get this mode to work...

Have a cold beer, and try one more time. Pull the connector out so you have a bit more room to work.

wurgs · December 5, 2015

Big thanks to Wurgs for the diodes. Looking forward to completing this mod soon.

No problem. Hope install goes smoothly.

GMC-AT · December 16, 2015

Anyone done this on a 2016 Sierra? worked great on my 2014. But I went to to plug in on the 2016... and the fog light plug didn't have a wire in it.

Spurshot · December 18, 2015

Anyone done this on a 2016 Sierra? worked great on my 2014. But I went to to plug in on the 2016... and the fog light plug didn't have a wire in it.

GM Upfitter website doesn't have electrical schematics for the 2016. I don't know of any way to figure this out for the 2016 other than a test light and a bunch of circuit testing.

GMC-AT · December 19, 2015

thanks for the reply. I appreciate you reporting back when the diagram becomes available.. I guess we will have to figure it out eventually....

webshopper · December 28, 2015

RE: Topic 162734-Foglights On With High Beams

I’m new to the forum this week, so please excuse any oddities from not knowing how to post.

Just purchased a Chevrolet Silverado 2015 2500HD LT and completed the “Foglights On With High Beams” modification successfully. I did study the GM 2015 and 2016 Upfitters Guides extensively. The 2015 Guide is 898 pages; the 2016 Guide is 1,617 pages so now there is a lot more information. The BODY BUILDER MANUAL FOR 2016 CHEVROLET SILVERADO/GMC SIERRA ELECTRICAL SECTION is available at:

https://www.gmupfitter.com/files/media/photo/664/Sierra_Silverado_Electrical_Body_Builders_Manual_Service_Manual_2016_en_US.pdf.

If you can't navigate to that, Google "GM 2016 Upfitter Guide" or key in "https://www.gmupfitter.com/pdflists/view/36". Choose the "Full Size Trucks/SUVs" folder.

For my application, pages 872 and 873 of the 2016 Guide apply.

For those not inclined or wish not to study diagrams, match colors on wires, and read the fine print, I offer these tips:

Perform your work in a dark ambient light and use flashlights. It’s easier on your eyes.
The X5 plug (brown color) inserted in the K9 Body Control Module (BCM) can be a bit difficult to remove but do not use tools; keep the locking tab pressed firmly and use your fingers to rock the plug.
The harness is tight but don't be tempted to cut the black fabric protection layer.
The connections you'll be making are ground so no heat is generated on the leads.
I sharpened the leads of the diode to produce a needle-like effect. This seemed to aid in insertion of diode leads into the proper plug holes.
The diode must be oriented properly with the cathode (striped end) placed in hole #18 (Brown/Violet stripe) Headlamp High Beam Relay Control. The anode (non-stripe end) is placed in hole #10 (Brown solid) Fog Lamp Relay Control.
The leads of the diode, when inserted properly, go into the plug ¾ of lead available on a standard 2¼" length diode.
I did not use any heat shrink or insulating tube. If you do, it may disallow smooth bends in the leads that remain external to the holes.
The vehicle battery was not disconnected.
Like any job, good tools help. I used a small needle-nose plier with a 45° nose bend.
I did go to Radio Shack® for the $1.49 package of two diodes show in the photo. I like the NTE® brand.
It does help to have the X5 plug (brown color) disconnected so that you can hold it while applying pressure to the diode lead while inserting. The leads bend extremely easily so take little bites with you needle-nose pliers. Don’t fight it or the lead will bend. If it doesn’t go, try another corner of the hole. To save on diodes, practice with a similar diameter wire.
The color of the #10 wire did change from Brown/White to solid Brown somewhere along the production line.
The above reflects only my personal experience and does not imply your particular situation will be the same.

I hope these hints help. I'm not much of a forum writer so please excuse the simplicity and the rambling list.

A special thanks to all that designed, contributed, and assisted in the 25 pages of this thread. Read the entire thread for special nuggets that might apply to your project.

All the best from Maine.

polarys425 · December 28, 2015

i used the 10-22. this runs the fogs off of the parking lights. be aware that once you do this you have no control of the fogs. there on automatically with the parking lights.

Wiring a switch in series with the diode would allow one the ability to reverse and enable this mod on command. That's my plan for tomorrow on my newly purchased '15.

Edit: Decided to get this done tonight. Had the usual trouble getting the pin of the diode in the connector. So, I changed it up a bit, using two stick pins with ball heads. These slide right in without trouble at all, making removal and reinstallation a breeze. At the other end of the wire is a simple switch so I can turn this mod on and off as needed.

Edited December 29, 2015 by polarys425

GMC-AT · December 29, 2015

So this will work on the 2016?

GMC-AT · December 30, 2015

ok.. I got it working on my 2016 GMC. Just so there is confusion.. everything is the same as the 2014-2-015. Just the one wire is a sold brown now on the 2016 as mentioned above. But the position ( where to insert the diode) is the exact same as seen on page 1 of this thread.

Truckerado · January 3, 2016

Got a 2014 silverado & am about to install some Rigid SR-Q2 LED's into the fog light assembly, this guide plus a set of fabbed connectors will help a bunch to make the install right, thx Spurshot!