Trailer wiring issue
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Joined: Nov 2012
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From: East Tennessee
Trailer wiring issue
I need some insight on a trailer wiring issue I'm working on. I replaced the 7-pin wiring harness end on our trailer this weekend but can only get running lights on the trailer, when hooked up to a 2004 Expedition. When either turn signal is turned on, both lights blink on the trailer on the running light filament. I can get no brake lights on the trailer at all.
I've tested the connection on the truck with a test light and all posts on it work correctly. I've tested all wires going back on the trailer with a battery booster to make sure I'm getting power all the way back and all of them work correctly. All of the trailer towing fuses are tested and good.
I've hooked the trailer up to my F150 and everything works fine, when hooked to it. So, I'm assuming that it must be something in the Expedition. It's wired from the factory for towing. So, is it a possibility that one of the pins is loose in the truck's connection? I'm figuring that the trailer towing relays are good or I wouldn't have anything at all on the trailer. If one of the pins is loose or something on the truck side, would that cause the weird things on the trailer lights, like I'm getting?
I've tested the connection on the truck with a test light and all posts on it work correctly. I've tested all wires going back on the trailer with a battery booster to make sure I'm getting power all the way back and all of them work correctly. All of the trailer towing fuses are tested and good.
I've hooked the trailer up to my F150 and everything works fine, when hooked to it. So, I'm assuming that it must be something in the Expedition. It's wired from the factory for towing. So, is it a possibility that one of the pins is loose in the truck's connection? I'm figuring that the trailer towing relays are good or I wouldn't have anything at all on the trailer. If one of the pins is loose or something on the truck side, would that cause the weird things on the trailer lights, like I'm getting?
Postmaster
Joined: Sep 2010
Posts: 3,472
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From: Southern Cal
I also agree with what sounds like a poor ground. I would spray some wd40 into the connector and plug in and out 5-6 times to rub contacts to ensure good connection.
If this doesn't work, look under your Expy's rear right side. The ground for this connection is attached directly to the frame (easy to see).
It is however, a crimp connector and it may be necessary to remove and clean and /or replace.
If this doesn't work, look under your Expy's rear right side. The ground for this connection is attached directly to the frame (easy to see).
It is however, a crimp connector and it may be necessary to remove and clean and /or replace.
Postmaster
Joined: Sep 2010
Posts: 3,472
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From: Southern Cal
He didn't indicate he did anything with his Expy.
Fleet Owner
Joined: Apr 2008
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From: 0,0,1
Who says the other truck is wired correctly?
Postmaster
Joined: Sep 2010
Posts: 3,472
Likes: 2
From: Southern Cal
What's the chance you use another truck and the wiring is also incorrect ?
We don't know much about the other truck but the chances of two vehicles wired wrong but happen to have aligned terminals properly is about the same odds as Winning the Powerball.
Check your ground.
We don't know much about the other truck but the chances of two vehicles wired wrong but happen to have aligned terminals properly is about the same odds as Winning the Powerball.
Check your ground.
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kailor
1997 - 2006 Expedition & Navigator
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Sep 4, 2011 12:22 PM
