I�ve got an ongoing problem with the tail lights on my trailer, and am having problems tracking down the source.

The normal �lights on� tail lights on the trailer will not work, although the brake lights and turn signals still do. When I turn on the lights in the truck, the wiring harness on the trailer gets hot, and the 30A fuse for the towing tail lights blows under the hood of the truck.

This problem first appeared a few weeks ago, and I thought I had fixed it by replacing the fuse and installing new Optronics LED tail lights (the old lights had some bare wiring that was causing a short).

The problem resumed this weekend. I�ve checked the visible wiring on the trailer, and I do not see any bare wires. It seems to have started up when my buddy backed the trailer down into the water a bit farther than usual � the side lights on it are not sealed LEDs. However, the trailer is all dry now, and it�s still heating up the wires and blowing fuses. The lights along the right side of the trailer will come on faintly (just the side light and the outside of the tail light) but the left side stays dark, until the fuse blows. Wires on both sides are hot, all the way down to the tail lights.

Any ideas?

I suspect I�m going to have to replace the whole harness � just hate to do it. It�ll take up a Saturday when I could be fishing.

It sounds like the lights on the trailer are the culprit. I've had the same issue with my boat many times. Either try to blow the water out and let it dry or better yet just replace it with a submersible lights. You shouldn't have to replace the whole wire harness if it the insulation looks good.

Thanks ... I will give it a try this weekend, when it has had a week to dry out. If it works then, I can be sure it's one of those side lights, since the rear lights are sealed. I would have replaced the side lights ... but they seem to be riveted to the trailer.

Try unhooking all your trailer lights, or aleast the side running lights. Then hook them back up one at a time, turn the lights on after each one. This might find the one that is causing the problems.
If you submerged your non-submergible lights while the lights where on then it could have heated it up enough to damage the light causing it to short out now.
I always unplug my lights before backing my trailer into the water. Even if you have submergible lights you my have connections that are not water tight and will short out through the water.
Also make sure you have a good connection where the pickup and trailer plug in. Take a pair of needle nose pliers and close the female contacts on the pickup plug. Resistance=Heat
Good Luck

check the ground wires on both truck and trailer plugs, i had similair thing happen to me a few years ago, it was blowing fuse under the hood ($5 a pop), turned out to be the ground on the truck side. made good connection onto truck frame problem solved

It turned out to be a short in one of the "clamshell" connectors for the side marker lights. I went ahead and paid the marina to replace the harness while I was out on the lake Saturday. It's just too durn hot to do anything outside except have fun.

I have never seen a light short out and blow a fuse. It is normally something in the harness / hook ups. I have all submersibles and when they start to leak water the bulb blows and nothing else. In fact it just happened and I need a new one right now.

Fuses, trailer lights, wiring, and all the connections along with the hard to access part of it can all add up to be a pain. Sometimes I find it easier just to turn it over to a shop and have them look at it. I had a similar problem but my wires turned out to be cracking and exposing them which caused a short everytime it hit the metal. Found the $ I paid to the shop to rewire was well worth it, no fishing time lost.

Have you had the trailer worked on lately? I bent a fender on a trailer once and they did a little welding when I had it fixed. The heat burned a wire and later I had the same problem as you are.

I think what happened in my case was that the little blue "clamshell" connector that tied the wiring harness into the side marker light had a piece of metal touching the frame of the trailer (it had worn through). I could not find it myself, and it was frustrating the heck out of me. By the time the shop got it, the wiring on that side was sticking to the trailer. They did a good job, and it was nice to have the work done while I was out on the lake in my boat.

Those are not fun problems to find..I had a rock or something ,nick a wire that ran across the back, and the wind or a bump,would cause it to bounce into the frame..bang, blown fuse..after looking and using the "Circuit Tester" I finally found it...

the best way to fix a trailer lighting system when it starts to fail is just do trhe whole thing because once the start they dont stop let me know if you need a hand i can rewire those things in no time