Hot Trailer plug

[Dennis L]

What pins should be hot on the trailer side of the 7-way plug? (Hot when not connected to tow vehicle)

New 2021 Shockwave Toy Hauler w/new 12 volt only refrigerator, solar, and two 6-volt batteries. When connected to tow vehicle - 2002 Silverado 2500HD - reverse lights come on tow vehicle unless RV's battery switch is off. Tester reveals center pin on trailer side of plug hot with RV battery switch on, and not when switch off (again, RV not connected to tow vehicle).

Obviously the center plug of tow vehicle is wired for reverse lights, which is confirmed with tester. I'm told issue is related to the age of my tow vehicle.

I think center plug is either for reverse lights or auxiliary power, both of which should power trailer from tow vehicle? and RV shouldn't send power back to to tow vehicle? Or has something changed with new trucks and/or is there simply an adapter I need to properly connect the two due to age of tow vehicle?

I know I could just disconnect reverse wire from tow vehicle side plug but want to confirm this is normal and not issue with trailer wiring.

Thank you!

[5picker]

Maybe this will help...

[phipps33]

#4 pin is the only pin that should be hot on the trailer end when disconnected from the TV.

It will draw the 12v from the battery/converter.

[CHICKDOE]

sounds to me as if the aux line and reverse light wires are crossed somewhere in the trailer. none of the wires in the 7-pin cable for the various lights or brakes should get their power from the trailer. they all get their power from the truck. i'm assuming the trailer reverse lights come on without the truck being in reverse. if so they must be getting their power from the aux line which is being powered from the truck. so quick testing with a meter can confirm this.

assuming they are crossed in the trailer there is probably a junction box up by the pin box where the 7-pin cable connects to the internal trailer wiring. you could open it and switch the aux and reverse lines. or if still under warranty have the dealer do it if he can do it in a reasonable amount of time.

[phipps33]

Originally Posted by CHICKDOE

none of the wires in the 7-pin cable for the various lights or brakes should get their power from the trailer. they all get their power from the truck.

Not true. The #4 pin will be hot from the trailer as it should be connected to the battery.

[CHICKDOE]

I was referring to the wires that operate the various lights, specifically the reverse lights, and the brakes. These are all powered from the truck and not the trailer. You are correct that the aux charge line is connected to the trailer battery positive terminal.

The issue here still sounds like the reverse and aux charge lines are reversed in the trailer. A good test would be to measure voltage at the battery terminals:
- Unconnected to the truck
- connected to the truck but not in reverse
- connected to the truck in reverse

If the voltage at the batteries increases when the truck goes into reverse that would confirm the reversed wiring.

[pgandw]

Originally Posted by CHICKDOE

I was referring to the wires that operate the various lights, specifically the reverse lights, and the brakes. These are all powered from the truck and not the trailer. You are correct that the aux charge line is connected to the trailer battery positive terminal.

The issue here still sounds like the reverse and aux charge lines are reversed in the trailer. A good test would be to measure voltage at the battery terminals:
- Unconnected to the truck
- connected to the truck but not in reverse
- connected to the truck in reverse

If the voltage at the batteries increases when the truck goes into reverse that would confirm the reversed wiring.

That is surprisingly common. Some years back, I remember reading articles on trailer wiring that said the center pin on the 7 pin connectors was 12V+, not for reverse lights. That there are miswired trailers out there does not surprise me. I would have been one of those except at the time my pop-up used a 6 pin plug. Luckily, the diagrams for 6 pin all said the same thing when I had to rewire the pop-up.

Fred W
2019 Flagstaff T21TBHW A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time

[5picker]

Originally Posted by pgandw

That is surprisingly common. Some years back, I remember reading articles on trailer wiring that said the center pin on the 7 pin connectors was 12V+, not for reverse lights. That there are miswired trailers out there does not surprise me. I would have been one of those except at the time my pop-up used a 6 pin plug. Luckily, the diagrams for 6 pin all said the same thing when I had to rewire the pop-up.

Fred W
2019 Flagstaff T21TBHW A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time

Those 6 pin plugs created a lot of confusion for the 7 pin crowd.
For as long as I can remember, the center pin on a SIX pin plug was 12v.
Many THOUGHT that carried over to a SEVEN pin plug and it doesn't.