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Discussion Starter #1 (Edited)
so the other day i hooked up me trailer and the brake lights turn signals all work but when i turned on my driving light i had no trailer light. Its the 4 prong connection. Any ideas? Thanks
 

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Discussion Starter #4
ill check both when i get home but its weird that it works with driving lights off then when i turn the lights on the trailer lights dont work
 

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Figure it out? I had the same problem you mentionsed and about pulled my hair out untill someone mentioned there was a seperate fuse for the trailer lights.
 

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Depending on where you live the 4 pin connector on the bottom of the bumper could me corroded as all get out. Also it sounds to me like you have a ground issue on the trailer itself.

Check to make sure all the lights are grounded right, I had to run grounds from the connector on the trailer to the rear lights to get the running lights to work right on my wave runner trailer.

Mike
 

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A multimeter or even a test light will tell you everything you need to know.
 

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I have had that problem with almost every tow vehicle I ever had. It is the ground on your truck. Most likely corroded or not installed properly.
 

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Ok, If on a straight wired trailer like a cargo or flat bed or boat trailer or some travel trailers where the battery on board the trailer doesn't help power the lights.....Then this is 9 times out of 10 a ground issue. The ground connection is just good enough to run the break lights etc but when adding the load of the running lights, the ground "snaps" and all the lights go out. This can easily be assessed buy taking a piece of wire and either through alligator clips or using a clean bolt area to ground from and running the wire in the same manner to the trailer. This makes a better clean ground and the lights should then all work. Now if you have a ground wire running from your trailer plug on the tow vehicle to the trailer, you need to clean up where it connects to the trailer frame or run a new ground. In ball hitch trailers where it is grounded through the ball, you need to run a good ground wire from your tow rig to your trailer.

If the fuses are blowing then the same thing can be happening above and the same assessment can be done with a clean ground. If the ground doesn't fix the problem of blowing fuses, then it is most likely a short in the trailer wire where the positive side is hitting the ground. This could be in the wires or in the light it's self. This will be a long process and I would start by pulling the bulbs. Then turn on the lights and if the line blows it is most likely a bad wire. If not then start putting in bulbs till the fuse blows then you know which socket is bad.

If you have a trailer that the batteries in the trailer help the trailer lights (usually longer trailers or 5th wheels) then god help you because it could be any number of things. Best bet is to get a good battery, separate from your tow vehicle, and set it next to the trailer plug on the trailer and start plugging (FUSED) wires in and see what blows and how.

With in my friends and family we have about 20 trailers of all types and I am the only guy that knows wiring. I can't begin to tell you the horror stories.
 
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