TOPIC: Trailer Light Problems

My trailer (1996 model) has baffling problems with the lights.

The running lights work great, EXEPT WHEN I APPLY THE BRAKES, MY RUNNING LIGHTS GO OFF!!!!!!!

The brake lights and turn signals work fine.

I have added a white wire ground to the tongue of the trailer, and all the lights on the Grand Marque work fine!!

WHY do my running lights go off when I apply the brakes, and come back on when I release the brakes??

ALSO, when I turn on the 4-way flashers, they go crazy, blinking alernately (one side then the other--They do not flash together!)

I have no idea what to look for to fix these problems! My friends trailer works correctly on my car, so its not the car!!!!!!!!

First order would be to check both the lights for ground and the white wire. Next check the plug for corrosion and if all the points in the plug are in fact snug. Have you checked your bulb sockets? It may sound stupid but many lights made for boat trailer use have steel bulb sockets that rust very fast. I have replaced perfectly good looking lights because of rusty sockets. And some with hardly a years use.

Really targets bad grounding. If it's a tilt trailer run a ground wire to connect beyond the pivit point to join the sections with wire and not depend on a rusty bolt.

Grounding isn't always what it seems. Old trailers, as well as old cars and trucks, do not follow a color code like most of us are used to in modern times. So toss what you think you know about red, green, black & white out the window and get a continuity tester. You're going to have to draw your own schematics for your trailer.

When I worked in a truck shop, we had spaghetti nightmares come in all the time. International Trucks used to have 100% black wiring! All you had was on the wire was a painted/stamped white number every foot or two on the black plastic of the wire.

I would concur with the bad ground except in the case of a short

So it could be either. When you see 18-wheelers doing this blinking thing it is because some of the lights are grounding through the other wires. Your bulbs can be a source of problems. I've seen entire big rigs flash when a turn signal goes on. It's better than a Griswold Christmas!

One trick is to get a 12 volt car battery and use probes to send current to different circuits in the trailer plug. This eliminates the car entirely AND you can get to individual holes in the plug since it's not hooked to anything.

You can make your own jumpers leads. Get some multi-strand wire and put some large clips on one end for the battery terminal and small alligator clips on the other ends. Then you can push small nails into the trailer plug and clamp the alligator clips to the nail leads (option B: just strip 3/4 inch of the wire and bend the wire over and shove the silly thing into each hole). Then you can see what each wire is actually supplying voltage to. You can clean and change each bulb as needed and make adjustments to the wiring. My dad taught me in any electric trouble shooting situation, check connections and switches FIRST, then move on to inspect the wires. You could have two wires pinched together inside the frame or stretched around a corner.



Here are a few sites to help edjamacate you on troubleshooting.


AA1Car.com

Trailer Wiring Diagrams

This is one of my favs because he just rambles on and on like me hahaha...

Boat Trailer Lights

Had a similar problem [or 'short' or 'fault'] and read somewhere that many of the lighting housings are supposed to ground to the metal trialer frame, simply by being bolted to the trailer. In my case, the I ran an extra wire from the ground of the socket to a freshly drilled hole in the trailer. Everyhtin now works fine for me.

Thanks everyone. I now have places to check from your info like the light sockets, etc.

besides the ground situation, check/replace the bulbs themselves. make sure that there is no short within a bulb or that the two contact pins on the bulb are not shorting out on the sockets contacts.

Also remove one bulb then try the brakes,etc. Then remove the opposite bulb and repeat. By using only one bulb you might find the "offending" side.

beside -all of the above-....

have replaced the tower...it may need an in adapter for trailer harness..

Just a suggestion:>

you may..want to get away from the old wire harness, and just buy a replacement, and completely replace the harness with a new set. To add to that, if you upgrade your tail lights to the "standard" 5 inch round sealed tail lights (like they use on a tractor trailer) with a metal bracket with a rubber insert...if you, just upgrade -everything- you will eliminate many of the -faults- that happen with the grade -b- accessory's that are sold at -Boat-Box-Store.com

been there done that..just replace.