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Discussion Starter #1
I have brake lights
I have running lights
I have turn signals
I have turn signals with running lights on

When I hit my brakes with the running lights on the whole trailer goes black

I rewired the whole trailer last night- no dice
I cleaned all the contacts on every connecter- nope
I connected a new ground on the trailer- nothing
I changed all the bulbs- running out of ideas- same problem
I unwrapped all the harnesses and checked all connections- not a thing wrong


I'm guessing all that's left is it could be some fucked up trailer lights or somethin (they are the same style but 2 different kinds...)
 

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...you've check all the trailer connections direct from a battery and not thru the truck?

worth a shot....might find it's an issue with the tow rig and not the trailer.
 

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FWIW, I used to flat tow a buddie's CJ that we rigged up to use the CJ tail lights, and had a similar problem. Turned out to be a couple wires crossed/mixed up.

Pete
 

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Try connecting a jumper cable from the truck frame to the trailer frame. That way you can rule out a ground problem.
 

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Discussion Starter #5
pcorssmit said:
FWIW, I used to flat tow a buddie's CJ that we rigged up to use the CJ tail lights, and had a similar problem. Turned out to be a couple wires crossed/mixed up.

Pete
I think for some reason that the lights themselves might have crossed wires inside (or corrosion, etc). The are the el cheapos that you buy with a yellow and brown wire sticking out the back. I switched the wires around last night but I did both lights at the same time so it would've still been screwy.

Woody- I checked all the wires throughout the tow rig and everything was clean and hooked up properly, as were all the harnesses. Both sets of wires I tried on the trailer gave the same problem. Don't have a spare battery laying around :D

70~K5- I put a new ground in the harness to the trailer. I followed all wires (and checked their connections) through to the ground on the tow rig. I didn't see any issue.
 

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Bad Grounds?

Is there one common ground connection from the lights? Look for a pig tail lead with a screw connecting the ground from the lights to the trailer ground.

Usually when I have "brake lights work, tail lights work" when I put one the brake lights with the tail lights on... both go out... common point is the ground.

Perhaps BOTH (R & L) sockets are corroded... normally only see it on one side... but worth popping the bulbs out and making sure the socket looks good.

Tom :usa:
 

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bigdude said:


70~K5- I put a new ground in the harness to the trailer. I followed all wires (and checked their connections) through to the ground on the tow rig. I didn't see any issue.
I've been hauling around big rig trailers for over 25 years. For 10 of those years I might hook up to as many as 10 diferent trailers a day. The #1 problem I've seen in trailer lights was a bad ground. I made up a 25' long piece of 10 gague wire with spring clamps on each end. The type you might see on some small battery chargers. I'd use this to make sure I had a good ground if I had light problems. This gets rid of one possiblity in the chain and if it doesn't solve the problem you go on from there. By using a jumper like that hook it the ground from each light and see if any of they aren't grounding right. If you have a ground problem it will try and ground its self thru the other side of the lamp. Thats why you'll see all the marker lights flashing sometime on a trailer when the turn signals are on. The turn signals are grounding thru the marker light ciruit. I'm just trying to help here.
 

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Similar to what others have suggested, pull the truck up beside the trailer and make a short temp harness directly from one light to the receptor on the truck. If they work fine this way, you know it is the trailer wiring. This also makes it easier to swap wires and see exactly what you are doing.
 

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Discussion Starter #10
Thanks for all the help. I ended up wiring in a new harness from the vehicle to check and see if it was anything to do with the insides of the stock circle harness. In doing this the wire for the drivers side brake light broke about 4-5" up into the wrapping while I was stripping it for the new harness.

It broke in a place that was completely wrapped in electrical tape and inside the plastic sheathing. It looked like it had been cracked and started to split/fall apart a while ago. i'm just glad it broke because I would've never found it without pulling all the damn wires out.
 
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