Continuous duty solenoid to cut power to 7 pin trailer plug

RnA2021 · February 27, 2023

We tow a trailer with our 2021 GMC Sierra 2500 gasser. I read that the 7 pin trailer plug is always hot, even with truck engine not running. We had a continuous duty solenoid installed in our 2015 Chevy Silverado 3500 to cut power to the trailer plug when the ignition key was off. I would like to find the wire that goes from the power distribution centre to the trailer 12 volt, and another wire that I can use to trigger the solenoid to complete connection when key is energized. Has anyone done this on a later model truck?

Thanks,

Rick

Another JR · February 28, 2023

Are you aware of this type of product? It will do what you want without you having to do the wiring you are talking about.

https://www.bluesea.com/resources/1366

RnA2021 · February 28, 2023

Thanks Another JR. I had a Blue Seas ACR in my boat, as I had two batteries, and only a small alternator on the outboard. I wanted to ensure that I could start the main outboard after fishing, as draw from my fishfinder and radio. It did the job well. For our trailer, I have a roof mounted solar panel, and 2, 100 watt lithium batteries, so my interest is primarily on disconnecting power to the 7 pin plug when the truck is not running. A less costly solution is the continuous duty solenoid, but perhaps issues with hooking it up. Specs on the Blue Seas ACR indicates maximum current is 140 amps, but I believe a 170 amp alternator is standard on the gasser with a single battery. Thanks anyhow, I appreciate your response.

Another JR · February 28, 2023

Note that the ACR just passes the current of the circuit it is on - not the entire alternator output necessarily. The trailer circuit is 10 awg wire and there will be quite a bit of voltage drop at, say, 30 amps. You would fuse that circuit as well.

RnA2021 · March 4, 2023

On 2/28/2023 at 2:39 PM, Another JR said:

Note that the ACR just passes the current of the circuit it is on - not the entire alternator output necessarily. The trailer circuit is 10 awg wire and there will be quite a bit of voltage drop at, say, 30 amps. You would fuse that circuit as well.

I reached out to Blue Seas and they don't recommend an ACR due to lead acid battery in truck and lithium in trailer. It was recommend that I install a DC to DC charger in place of an ACR.

Another JR · March 4, 2023

I agree with them. I see now you said it clearly above, but I didn’t notice you were talking about a lithium battery being involved. I have a Victron 30 amp dc to dc charger I installed two years ago in my truck camper and am happy to answer questions about it and the wiring involved.

Edited March 4, 2023 by Another JR

Another JR · March 4, 2023

Picture of my dc to dc charger installation in my camper battery compartment.

RnA2021 · March 5, 2023

4 hours ago, Another JR said:

Picture of my dc to dc charger installation in my camper battery compartment.

Great install using quality components. I have a Victron BMV-712 to monitor my batteries. It would be a logical step to add a Victron DC to DC converter.

I suppose you ran wiring from your truck battery. I has been raining for a couple of days, and I did not look under the truck to run the wiring. What side did you run the wiring on? As I don't have an inverter and have 200 amps of batteries and 190 watt of solar, I would probably install the 18 amp version. My trailer came from the factory with a PWM solar controller, and would be challenging to run new wires for an MPPT controller.

Thanks

Rick

Another JR · March 5, 2023

I ran 6awg Ancor marine type 3 positive wire from the right side main battery fuse block across the top of the firewall along a factory bundle to the left side. I ran the 6awg negative wire from a large body ground post near the aux battery on the left side. Those wires then go down to the frame below the brake booster and run back on top of the left frame member alongside a large factory wire bundle. They then run up between the rear of the cab and the bed and over the top of the bed with a 2 foot pigtail and a booted SB50 connector. The entire length of both wires is covered with split loom sleeving. The camper has a mating connector and the same wire type all the way to the dc to dc charger.

The main reason to go down the left side is that the exhaust is on the right side on my GMC truck. Same reason the factory bundle is on the left.

I have 200 ah of lithium battery in my camper. I use about 30-35 ah per day depending on weather. I decided on a 30 amp dc to dc charger based on the idea that I can add another day’s worth of charge for every hour I drive. I considered going bigger but not smaller than 30 amps. The price difference between the 18 amp and 30 amp chargers is $170 vs $227.

I don’t know why you would need to rewire to change from a PWM charger to an MPPT charger. What are you thinking you need to change?

RnA2021 · March 5, 2023

18 hours ago, Another JR said:

I ran 6awg Ancor marine type 3 positive wire from the right side main battery fuse block across the top of the firewall along a factory bundle to the left side. I ran the 6awg negative wire from a large body ground post near the aux battery on the left side. Those wires then go down to the frame below the brake booster and run back on top of the left frame member alongside a large factory wire bundle. They then run up between the rear of the cab and the bed and over the top of the bed with a 2 foot pigtail and a booted SB50 connector. The entire length of both wires is covered with split loom sleeving. The camper has a mating connector and the same wire type all the way to the dc to dc charger.

The main reason to go down the left side is that the exhaust is on the right side on my GMC truck. Same reason the factory bundle is on the left.

I have 200 ah of lithium battery in my camper. I use about 30-35 ah per day depending on weather. I decided on a 30 amp dc to dc charger based on the idea that I can add another day’s worth of charge for every hour I drive. I considered going bigger but not smaller than 30 amps. The price difference between the 18 amp and 30 amp chargers is $170 vs $227.

I don’t know why you would need to rewire to change from a PWM charger to an MPPT charger. What are you thinking you need to change?

Good quality components with your setup.

Lance used about 10 gauge wire from the solar controller on the curb side of the trailer, and it then connects to the battery master switch on the street side of the trailer. I can't see the wire and hence it would be a task to run heavier wire for an MPPT controller.

Thanks for information on your wiring.

Another JR · March 5, 2023

The runs from your solar panel connectors to your solar charger and from the solar charger to the batteries are short, so 10 awg is fine for 30 amps without excessive voltage drop. My camper has 10 awg wire from the solar panels to the charger. You shouldn’t need to replace your solar system wiring.

With the long run from the truck to the dc to dc converter near the camper battery, voltage drop becomes an issue. The dc to dc charger raises the voltage to the camper battery for charging, but if the drop on the input side is excessive the charger has to keep stopping to check if the engine is still running, unless you run a separate ignition on signal to it. It’s better to just run adequate wire gage from the truck. 6 awg for a 30 amp charger and 8 awg for a 18 amp charger will be sufficient for the Victron Orions to avoid charger cycling.

Another JR · March 5, 2023

Deleted double post

Edited March 18, 2023 by Another JR

RnA2021 · March 17, 2023

How did you do the wiring at the 12 volt truck battery? Thanks

Another JR · March 17, 2023

My truck has two batteries, and I wired the camper to the main starting battery, not the auxiliary battery (planning to use the aux battery for an on board air compressor eventually). The main battery is on the passenger side and has a battery fuse block mounted on top of it. The fuse block from the factory had an unused 80 amp fuse and post, so I connected the 6 awg positive wire to that. It’s the wire with the red shrink tube at the lug. I connected the negative wire to a nearby body ground stud that was connected to the battery.

RnA2021 · March 17, 2023

11 hours ago, Another JR said:

My truck has two batteries, and I wired the camper to the main starting battery, not the auxiliary battery (planning to use the aux battery for an on board air compressor eventually). The main battery is on the passenger side and has a battery fuse block mounted on top of it. The fuse block from the factory had an unused 80 amp fuse and post, so I connected the 6 awg positive wire to that. It’s the wire with the red shrink tube at the lug. I connected the negative wire to a nearby body ground stud that was connected to the battery.

Thanks, look like an easily accessible location; I could mount a fuse on the firewall. My truck only has the right side battery, so I think I may identify the 7 pin charge wire from the under hood power distribution and add a 30 amp off-on switch, so that I don’t’ have two charge sources from the truck, plus solar on the roof. Sound like a good ideas?

Rick