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Dc to dc charging tie into 3500 battery/alternator

RE: disabling pin 4 on the 7-way

I've been informed that some tow vehicles may need to see power on this pin to properly 'sense' the trailer is attached.
I'm assuming this is not true (at least for my '23 2500) otherwise I would have seen reports of similar behavior here, but thought I would ask anyway.
 
cmelville42 said:
RE: disabling pin 4 on the 7-way

I've been informed that some tow vehicles may need to see power on this pin to properly 'sense' the trailer is attached.
I'm assuming this is not true (at least for my '23 2500) otherwise I would have seen reports of similar behavior here, but thought I would ask anyway.
Click to expand...
All vehicles that I'm aware of (and certainly our trucks) detect a trailer connection via the brake circuit. My trailer has no connection to the 7 pin power line and it works fine.
 
downsc123 said:
That was my first thought but it could not find a wiring diagram from the trailer (2023 Grand Design Reflection 324MBS) - anyone know how to disable on the trailer end short of pulling out the pin on the 7 way connector?
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Open the junction box that the 7 way pigtail goes into on the trailer. Disconnect the 12V+ feed there and cap with wire nut.

This leaves connections between the battery, house disconnect/12V distribution panel, and breakaway switch intact.
 
jsalbre said:
If I connect a trailer without brakes the truck doesn't register it.
Click to expand...

Same, even thou I could select a trailer without brakes for the trailer trip… engineers!

I believe newer Fords don’t use the brake circuit, but I’m not sure which one they use. Brake light resistance would be the smartest.
 
AH64ID said:
Same, even thou I could select a trailer without brakes for the trailer trip… engineers!

I believe newer Fords don’t use the brake circuit, but I’m not sure which one they use. Brake light resistance would be the smartest.
Click to expand...

Would that work with led lights ? Often that is the big challenge - circuits designed to detect a filament won't work with an led control circuit.
 
HarryN said:
Would that work with led lights ? Often that is the big challenge - circuits designed to detect a filament won't work with an led control circuit.
Click to expand...
My father's 2022 GM uses PWM pulses on the tail light circuit (and possibly other circuits) to detect and identify the trailer, even when running and/or parked (trailer theft alarm). Downside, you can't natively use the tail light circuit to power the rear view camera on your RV without adding some circuitry. My older ram is more rudimentary - DC power at least on the parking light circuit.

Even LED setups can be identified. I think our camper has 17 individual elements on the parking light circuit.
 
The 2025 trucks do detect a trailer based on lighting, I tried wiring my flatbed using a 7pin splitter like I had on my 2021 and the 2025 went into trailer mode from just Left/Right/Running/Reverse being connected through the 7 pin
 
cyclopsdiver said:
The 2025 trucks do detect a trailer based on lighting, I tried wiring my flatbed using a 7pin splitter like I had on my 2021 and the 2025 went into trailer mode from just Left/Right/Running/Reverse being connected through the 7 pin
Click to expand...
Interesting change. I wonder if that will cause issues with trailer cameras like it does on GM trucks.
 
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