wiring issue/ troubleshooting help

[motorboatinking]

I drive a 2013 Outback, and have a 1996 Jayco Eagle 8. My car only has a 4 way trailer harness, and the trailer has a 7 way plug. The owner before me only had a 4 way vehicle, so he added a 4 way plug to the trailer, and literately zip tied brake lights to the rear of the trailer. I want to use the trailers lights, so I bought an adapter, but I am having issues. The front lights on the trailer work correctly, but all the lights on the rear of the trailer do not. I took a bulb out and swapped it with the front, and the rear still did not work, and the front did, so it's not the bulbs. I am getting about 5 volts to the brake lights when the vehicle brakes are hit. I'm not sure if that is enough or not. How do I go about trouble shooting from here?

Also, the trailer does not have brakes, and I am not concerned with a 12v hot wire, unless that is the issue, so the three wires coming off the adapter are just there. I did ground the adapter and it has continuity to the negative terminal car battery. Also, the trailer has a battery and it is hooked up.

[dennis b]

First since you have the 7 way plug on trailer and battery is hooked up, take a wire and jump#3 & #4 terminals (12v & taillights) lights should come on all way around. this will confirm that you have power going back to them, and would mean plug on vehicle is not wired right.
If that is the case you may be better off eliminating the 4 way from 7 way and rewire 7 way from scratch.
I'm a novice with elec. problems, but this is where I would start.
Sure there is someone here a lot smarter!

[dennis b]

OH... and welcome to JOS!

[motorboatinking]

The adapter has three wires on it, one for 12v hot, one for a brake controller, and one for reverse lights. The trailer doesn't have reverse lights or brakes, so I don't need those. For the 12v hot wire, do I need to wire it to the car battery, or could I wire it to the trailer positive terminal for 12v. It would be a much shorter distance and a little easier.

[dennis b]

adapter?

[Matt Chapter]

Wiring problems are often frustrating but with patience they can be solved. First you need to understand what your goal is. In this case, you want to use the trailer brake lights. Given that the PO wired in new brake lights, I wonder if they reused the old wiring. You should try and figure out how those are wired, it could be helpful information.

So, given that you don't want reverse lights, 12v power, or brake control, you really only need the 4 pin connector to make the proper connections from the TV to the trailer.

You will probably want a multimeter so you can test for voltage at each point. Start at the TV plug, and verify that you have voltage in the correct cases, i.e. turn on your vehicle lights and check for approximately 12 v on the running light pin. Then you can check at other connections for 12v all the way back to the lights, including the fixture itself.

[Mustang65]

After rereading your issue a few times, I would take the leads from the back lights apart. You may have corroded wires which would explain why there is only 5 volts there. Get some electrical contact cleaner, remove the wires, clean the wires and re-terminate them in new wire nuts. Check to see if where the lights connect to the TT's ground is OK? Check the bulb contacts in the light assembly to see if they are clean, a pencil eraser will clean them for a test.

Another place to check is in the 4x4 electrical box at the front of the TT, where the TV's cable terminates. You may find something there.

See if that does anything.

Just my thoughts,

Don