Trailer wiring problem
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Joined: Sep 2008
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Trailer wiring problem
2003 F250 7.3L PSD crew cab. I pull a boat trailer using the 4 pin connection to the trailer. When I hook up the lights, only the trailer side lights and bright (brake) tail lights work; no parking lights and no turn signals on the trailer. This is only when the parking lights are on in the truck. If truck lights are off, the trailer has NO brake lights or turn signal lights. In other words, the truck parking lights make the trailer brake lights come on.
The truck lighting system works perfectly. I thought I had a short in the trailer wiring but when I checked the 4 pin plug on the truck, the tester shows the same thing - no turn signals only brake lights with the parking lights turned on.
SO... it seems my truck has some wiring problem between the truck lights and the 4 pin plug. I'm at a loss on what to do next or how to fix.
HELP! Please.
I've owned the truck since new. No modifications from the factory. It's worked perfectly until now.
Thanks,
Homer
The truck lighting system works perfectly. I thought I had a short in the trailer wiring but when I checked the 4 pin plug on the truck, the tester shows the same thing - no turn signals only brake lights with the parking lights turned on.
SO... it seems my truck has some wiring problem between the truck lights and the 4 pin plug. I'm at a loss on what to do next or how to fix.
HELP! Please.
I've owned the truck since new. No modifications from the factory. It's worked perfectly until now.
Thanks,
Homer
Post Fiend
Joined: May 2006
Posts: 10,007
Likes: 4
From: Central Florida
So key on, parking lights off.
No turn signal, no brake, no parking lights.
Key on, parking lights on
No Turn signal, no brake, yes parking lights
or
All lamps are on?
First thing I would check is the continuity of the white wire to ground. The white wire provides a ground, you can also ground a trailer through the hitch if it's clean enough and the trailer is wired so.
Then the Green wire should have 12v when the brake is pressed. It should also pulse if the turn signal is on. I think this wire runs the pass side.
The yellow wire should have 12v when the brake is pressed. It should also pulse if the turn signal is on. I think this wire runs the drivers side.
The brown wire should only have 12v when the parking lights are on.
Use a good chassis ground to test these and not the one in the harness. It's possible you have a grounding issue.
No turn signal, no brake, no parking lights.
Key on, parking lights on
No Turn signal, no brake, yes parking lights
or
All lamps are on?
First thing I would check is the continuity of the white wire to ground. The white wire provides a ground, you can also ground a trailer through the hitch if it's clean enough and the trailer is wired so.
Then the Green wire should have 12v when the brake is pressed. It should also pulse if the turn signal is on. I think this wire runs the pass side.
The yellow wire should have 12v when the brake is pressed. It should also pulse if the turn signal is on. I think this wire runs the drivers side.
The brown wire should only have 12v when the parking lights are on.
Use a good chassis ground to test these and not the one in the harness. It's possible you have a grounding issue.
Hotshot
Joined: Feb 2003
Posts: 11,537
Likes: 27
From: Long Beach, Ms.
No short in the trailer but maybe improperly wired? Trailer Wiring Harnesses Troubleshooting - etrailer.com
http://www.etrailer.com/faq_wiring.aspx
http://www.etrailer.com/faq_wiring.aspx
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