Troubleshooting Boat Trailer Wiring with 4-Way Flat Connector

Question:

I replaced the trailer 4 pin plug to the existing wires which had previously worked properly except for a poor ground connection. I connected brown to brown, white to ground. On the trailer I had a red wire that I connected to either the yellow or green wire on the plug. I cant remember which. And the 4th wire Which I believe was green I connected to the green wire on the plug. The results of all that is that I have no tail lights or turn or hazard lights. But I noticed while driving the running lights and possibly the tail lights come on when I apply the brakes. Any suggestions other than starting over using the old trial and error method?

asked by: Pete F

Expert Reply:

Unfortunately, it sounds like you may have a ground issue still. The brown wire is normally your running lights, the green is normally the right turn signal and brake light, the yellow (which sounds like red on your trailer) is normally the left turn and brake light, and then you have the white ground. The reason I think you have a ground connection is because you seem to have some lights working and nothing at your taillights. The taillights often have a separate ground wire that needs to be connected bare metal to metal on your trailer, however it is not uncommon for that ground connection to be in the mounting hardware of your taillights. It sounds like this may be the issue. I recommend starting there and making sure you have a bare metal to metal connection at each taillight.

If that doesn't solve your issue, then I recommend using a circuit tester like # PTW2993 and testing the pins on your vehicle first. Next, connecting your trailer and testing each wire on the trailer side of that connection, and then finally testing the connection at each taillight for each wire. If you have power at the vehicle side, and then the trailer side of the connector, but not at the taillights, then probing the insulation for a short every few feet is your best option to find the short. It isn't likely you have three shorts, so that is why I recommend checking the other options first.

expert reply by: Jason S