Trailer Light Problem

I have been having problems with my trailer lights all year so yesterday I decided to start all over and put on a whole new setup. My new problem is everything works EXCEPT when the lights are on and I step on the brakes everything cuts out. The brakes lights work when the running lights are not on but when they are I get nothing. Otherwise all signals and lights work. I did hook-up my neighbors truck as well with the same results, so I know it is not in my truck. Does anyone have any ideas or suggestions on what I should try?? Thanks!

Make sure it is grounded

The first thing I would look at is the ground on the trailer. No rust around the screw that grounds the wires. Grounds are very important on trailers.

Looks like we posted at the same time.

I thought of that also. I did grind and sand the spot down to bare metal.

I’ve got to agree with the others here. Did you have the trailer on the hitch? If not, that’s your problem.

Also, if it is a tilt trailer, make sure there is a good ground where the trailer pivots.

Gator Hunter

Double check to make sure you don’t have a 5 wire harness going to a 4 wire. Sounds to me that you just have the wires not going to where they belong. Take a circuit tester and check the truck harness with the trailer harness and make sure they match up

The last time I wired up a trailer, I ran a dedicated ground wire all the way from the light assemblies to the connector. I’ve stopped relying on questionable metal-to-metal connections in the trailer frame and the ball to make that part of the circuit.

Muskyman is onto something here……….

I have a basic knowledge in spark……….

I spent about 3 hours trying to fix and “rig” the wires for a trailer to my fathers ford van. I was just short of burning the whole thing down on purpose, because of frustration…….

I would wire one way and have running lights, but no brake lights, then another way: brake lights and running lights, then no turn signal………..On and on and on……….again, after 3 hours…………..get a torch……..

So, I called a buddy of mine who works at an auto shop and he called me an idiot for not calling him sooner………..

Depending on the type of vehicle, some require “adapters” in order to make everything come alive. It has something to do with having brake lights within your running lights or having separate bulbs for the brakes and running lights on your vehicle……………

Call a reputable auto parts store and tell them your vehicle and they will make sure you have the right plug………

Then, take a test light and run it into the plug to find out what wires come alive from what light (brake, running, blinker) on your vehicle………….Then run those wires to your correct light on your trailer and you are good to go………

Or just count the number of bulbs on the back of your vehicle. If there are seperate Turn Signal and Brake Light bulbs, then you need an adapter. I first encountered this particular problem with a 1983 Ford sedan. I found an module at Crown Auto for $10.00 and I was in business. It has 5 wires on the input side: Ground, Running lights, Brake lights, and each Turn Signal. On the output side are the normal 4 wires: Ground, Running lights, and the two Turn Signals. It was a little extra work to install but worked perfectly on the next several vehicles I owned.

If you’re aplication is a flat four, I believe the green is rite, yellow left, and the the brown wire(s) are secondary ground for the flasher relay witch are grounded through the light assembly, if one of the brown wires comes disconnected it will cause the lights to cut out when the breaks are applied as well as no signal flash. Some times on a double grounded setup where the white wire is grounded on the truck as well a the trailer, if one comes loose or corroded it can have the same effect.

Another thing to check is the tail-lights. Some lights have their own ground wire that must be grounded to some cheap metal in which the light is mounted to. I to had problems with my trailer and it took hours to find the little bugger.

I have the same problem, my lights work, blinkers work but as soon as I put brakes on, lights go off. It used to be just one side but now its both! I couldnt figure it out so I just put more insurance on my boat…just kidding!

I did get them working. Hatchetman you were correct, I needed to clean and scrape the mounting brackets so the ground on the light itself was good. Thanks to everyone for the help.

Another happy IDA member!