trailer light issue

Replaced the plug on my trailer because it had gone bad due to salt.

Get everything wired up and check the lights. The left side is working 100% but the right side only the indicator light would work not the brake/turn signal.

Replace the bulb on the right side and now it works as it should. However now the left side brake/turn signal will not work. Any idea why this is? My understanding is that each side of the trailer is wired separately.

The trailer is wired with 6 wires (3 down each side) the plug has 4 wires (brown, green, yellow, white). There are 2 brown and 2 white wires coming from the trailer. They are twisted together and crimped in a butt connector. Could it be an issue at the crimp location?

Yes. Solder it and heat shrink for a good seal.

mxskeeter wrote:

Yes. Solder it and heat shrink for a good seal.

Ok. No other area there could be a failure other than at the crimp?

There could be a failure anywhere in the wires.
Mice chew
wires rub on the frame while driving
ground connections rust and break the circuit

When you are fighting these issues its best to rewire the whole thing. I suggest learning how to run a specific ground ware to the lights rather than using the frame as a ground. Also solder will trump any crimp connector unless you are going for speed of install in a pinch. Also learning how to use a multi meter will help to diagnose issues.

mark-bruzek wrote:

There could be a failure anywhere in the wires.
Mice chew
wires rub on the frame while driving
ground connections rust and break the circuit

When you are fighting these issues its best to rewire the whole thing. I suggest learning how to run a specific ground ware to the lights rather than using the frame as a ground. Also solder will trump any crimp connector unless you are going for speed of install in a pinch. Also learning how to use a multi meter will help to diagnose issues.

Sure. But does it not matter that the right light worked fine until I put a working bulb in the left? I’m an amateur for sure but I guess this leads me to believe the only area the right and left side are related is at the crimp where they are crimped together.

It more than likely is a ground problem. The white wires are your grounds and most often they use the trailer frame as a ground but if you have a white wire running down each side they might not be using the frame for a ground. The first thing I would do is check all the grounds and make sure there connections are good and if they are hooked to the frame that there clean tight connections.

I’ll second what Bryan said, bad grounds can cause all kinds of issues. When I rewired my trailer, I connected the white wire from harness to lights and also to frame. Making sure your hitch ball is clean doesn’t hurt either. My camper must have a bad ground somewhere that I haven’t found yet, after cleaning the inside of hitch and the ball the lights work fine. Still looking for the bad ground.

But before you dig too far in there, first thing I would do is disconnect the trailer lights from the vehicle and plug in a flat-4 test plug into the trailer connection at the vehicle. Make sure your vehicle is properly “sending” the power back to your trailer bulbs. If not, start with fuses.

Beyond that, I agree that trailer issues are USUALLY ground issues.

A lot of newer vehicle equipped with OEM trailer harnesses have separate fuses for the trailer wiring. I know Chevy has fuses in the box under the hood and I think Ford has them below the glove box. If you can’t find the tester that pool2fool recommends by a test lamp as normal low impedance volt meters can be deceiving

I got it figured out guys. Pulled the bulb and put it back in. It’s working now so must of been a wonky connection