Brake Light Problem

[BlaznLow]

Just installed a new trailer light system. Inside the van was all professionally done and then my friend asked to do the trailer. The lights work fine when the headlights are off but when they are on. There is nothing. I have read alot that its a bad ground but i literally ground all new fresh bare metal.
I have run out of ideas of what to look for. Any help/suggestions please

 

[generator12]

Re: Brake Light Problem

"The lights work fine when the headlights are off but when they are on. There is nothing."

Not sure I get what you're saying. The trailer lights work if the parking/marker lights are on? Obviously there will be no trailer lights with all vehicle lights off except for brake and turn signals. Do they work at all?

 

[bruceb58]

Re: Brake Light Problem

its definitely a bad ground. You grounding the vehicle to the trailer through the wire harness?

 

[BlaznLow]

Re: Brake Light Problem

where the trailer plugs into the van. the wire harness has a ground to the tongue. Each light has its own ground. (which all have been ground down to bare metal via disc grinder) Plus when the trailer is hooked up. Shouldnt the trailer now be ground to the van?

Ill recap. headlights off. turn signal/brake lights work on both trailer and van.
when headlights are turned on. trailer lights dont work period and turn signals blink super fast on van.

could it be a blown fuse or not big enough fuse?

 

[bruceb58]

Re: Brake Light Problem

Easy way to test it! Just get a battery jumper cable and attach one end to the frame of your vehicle and one end to the the frame of the trailer(bare metal) and see if your problem goes away.

 

[generator12]

Re: Brake Light Problem

First of all, this thread will surely be moved to the trailering section. No harm, just warning you.

The fast blinking of the turn signal interrupter indicates a high current draw. Since it happens only with the headlights on, it's almost certainly a mis-wiring job somewhere.

And no, it's not likely to be a fuse if everything works at one point or another and you haven't replaced one.

I would get a DC voltmeter and, with the headlights off, disconnect the van from the trailer and determine which pins on the van's socket provide me with turn signals. You can use the van's emergency blinker to do this. Measure from each pin to a good metal ground and look for voltage turning on and off with the blinker operating. Write these pin colors down...! (If you don't have access to a voltmeter, a 12 volt light bulb with wires connected will do the job.)

Then I would turn the headlights on and see if the pins continued to operate the same way. If so, the problem is almost certainly in the trailer wiring. If not, they're in the van somewhere.

Sorry I can't tell you which color wires provide which services.

 

[bruceb58]

Re: Brake Light Problem

The fast blinking of the turn signal interrupter indicates a high current draw. Since it happens only with the headlights on, it's almost certainly a mis-wiring job somewhere.

Its actually a low current draw which is why this usually occurs when a bulb is burnt out.

Again, its the ground! With the headlights off, that path is being used as a sneak path ground. With them on, that sneak path is removed which causes the lights not to work. CHECK YOUR GROUND!!!!

 

[generator12]

Re: Brake Light Problem

Its actually a low current draw which is why this usually occurs when a bulb is burnt out.

Whoops! You're right of course.