Brake lights don't work on boat trailer when brake is applied.?

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JoeJ

Member
Ok, my first thought is that it is a bad ground, and i browsed through several questions here in which people had suggested bad ground, so that's probably the problem. It is a four wire system. My question is do you have to have BOTH the truck side wiring harness AND the boat side harness grounded, or will one suffice? Here's what i found:

It looks like in the wiring harness on the truck side, that the ground wire is cut. I thought that if i hooked the trailer side harness ground wire securely to the truck chassis that it would work, but it didn't... do BOTH ground wires need to be grounded for it to work? I thought that as long as the circuit has a ground (no matter from which side) it would work. Am i wrong?

Thx for any help.
ALSO: Do the tail lamp assembly's HAVE to be grounded as well for this to work? (i was doing some testing by just wiring the new lamp assemblys up to the harness and not attaching to trailer). If they have to be grounded as well, this is just accomplished by bolting them to the trailer, correct?
 
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johne

Member
All the trailer lights would use the same ground. Do any of the lights work? If nothing is working, it most likely is the ground on the trailer side.
Somewhere on the trailer there should be a wire connected to the metal with a screw. Make sure that connection is good. Also a 12V test light is very helpful in trouble shooting something like this. Make sure you are getting a signal at the truck plug first then plug it back into the trailer and start checking the trailer connections. I hope this helps.
 
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dusty_titus

New member
Did you check your fuses? - do your brake lights on the truck work? When you hook up your trailer and they BOTH don't work - there's a short somewhere. If your truck lights work and the trailer lights don't - Is it possible that your lamps in the trailer mountings are bad? Moisture in the trailer mountings are a common factor in the failure of brake/turn lights.
 
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BobW

Member
Take sandpaper and sand down the connections to your truck. Sometimes dirt can get in there, especially if the trailer is stored outside, and the dirt doesn't let the connections work
 
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