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Discussion Starter · #1 ·
I know the problem is with my truck because when I hook the same trailer up to a different truck it works fine.

On my trailer the four ways, and signal lights will work until I turn on the headlights. When I turn on the headlights the clearance lights will come on but the trailer lights will not come on and the four ways and signal lights will no longer work. When I turn the headlights back off the signal lights and four way flashers will start working again. I'm not sure why my clearance lights come on when i turn the headlights on but everything else stops working.

If anyone has any ideas please respond as I'm not sure where to go from here
 

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That is a strange problem. I agree that it might be a faulty ground. Try running a temporary ground wire from the trailer frame to the truck frame and see if the problem goes away.
 

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If you are talking about the 7prong plug. There are 2 different adapters. I think Dodge and GM use different plugs. I had to go to U-Haul and buy both 7-prong to 5-prong adapters. Figure out which one worked and then took the other one bacK for a refund.
Just an IDEA!
My 25cents worth of input. 2cents worth doesn't do it anymore. Inflation!!!!!!!!!
 

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I would try a bad ground first (after you're sure the pin-outs are correct. I had the problem a lot with my old enclosed trailer.
 

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i had a similar issue with my 99, ad it turned out to be a bad 7-4 pin connector, and another 7-5 pin fixed it
 

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Discussion Starter · #7 ·
If you are talking about the 7prong plug. There are 2 different adapters. I think Dodge and GM use different plugs. I had to go to U-Haul and buy both 7-prong to 5-prong adapters. Figure out which one worked and then took the other one bacK for a refund.
I tried running a ground from the trailer frame to the truck frame and it didn't correct my problem. Does dodge wire there 7 prong plug differently than GM Does? I got the trailer to work when I hooked it up to my old GMC but not with the dodge.

Also the Trailer has a 7 Prong connection so its not a adapter issue.

my truck also does not have electric brakes yet. The braking on the trailer is electric. Would this be a problem. I was just going to run it out to the campsite the first weekend without and then put elcetric brakes on it next week
 

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There is an industry standard for the pin-out of the 7 pin RV plug. All truck and trailer manufactures should be wiring the plug to this standard.

How old is your GMC? Is the plug on it wired from the factory or was it installed by someone? Do you have another trailer that you can hook your truck up to to test it?


Going back to your first post, your clearance lights should come on when you turn on your headlights.

If your trailer has electric brakes, you should have a controller before you tow it. There will be people that say you can tow it without them but it's a safety issue. In most states it is also law that trailers over a certain weight must have brakes. Your truck will still pull it without having the brake controller though.
 

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Discussion Starter · #9 ·
solved the problem tonight. The problem was on the trailer the sockets holding the dual filaments on the lights had a poor ground .. that is it had enough of a ground to run either the tail or brake lights but not a good enough ground to run both at the same time.. I cleaned up the the bulbs and the socket and both work fine now. it worked fine on my other truck with the poor ground , but my other truck ground wire going to my 7 way connector is about 6 times thicker wire and is grounded to the frame on the back of truck.... the dodge is just a thin wire ground that is grounded through that computer module, thus it is more suseptible to a poor ground I found on the internet that dodge used smaller wire for the harness , so you need real good grounds on what you are towing,which is why they suggested online running a separate ground wire from the towed vehichle to the battery ground on the truck, and use that instead of the computer small wire ground..there is no need to do this as you just have to keep really good ground connections on the towed trailer..

Now I just have to install a trailer brake control and I'm all legal. Thanks for the input guys
 
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