towing light problem

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Jul 19, 2015 | 08:23 PM

Mike Brackins

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towing light problem

when I hook a trailer to my '04 F-250 the parking lights stay on. The lights on the truck are not on. I pulled the fuse for the towing lights and they will go out. Pulled what I beleive to be the relay according to the owners manual and they still stay on. I have to unplug the trailer everytime I stop for any period of time. Now it has started blowing the fuse for the towing lights

Jul 20, 2015 | 07:26 AM

RV_Tech

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From: Bristol, TN.

Just to be sure I am clear, the parking lights on the truck are staying on or the marker lights on the trailer are staying on?

Steve

Jul 23, 2015 | 08:13 PM

bigredtruckmi

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From: Huntington Indiana

Sounds like his description is the trailer battery must be back feeding to the truck light system. Wonder if 7 way plug is shorted somehow on trailer side

Jul 23, 2015 | 10:59 PM

A Rodder

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Pull the case of the plug back and verify the top pins labeled black and green are not somehow touching.

(Black is hot, green is running /clearance /marker/ tail lights)

Jul 24, 2015 | 06:48 AM

RV_Tech

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I don't think the pin can be touching, but perhaps corroded or wires are loose. To know whether issue is trailer backfeeding, disconnect trailer battery, but leave seven pin plugged in. If you still have lights, plug is completing circuit somewhere on truck.

Pulling the relay should mean power back down that leg would end at relay receptacle. How is power getting to lights, unless it is shorting somewhere else? Don't know, just wondering out loud. Is trailer backfeeding down the ground perhaps?

Steve

Jul 24, 2015 | 09:52 AM

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Quote:

Originally Posted by RV_Tech

I don't think the pin can be touching, but perhaps corroded or wires are loose.

CORRECT, the strands of wires may be frayed and touching.

To know whether issue is trailer backfeeding, disconnect trailer battery, but leave seven pin plugged in. If you still have lights, plug is completing circuit somewhere on truck.

Great idea that's quick and easy.

Pulling the relay should mean power back down that leg would end at relay receptacle. How is power getting to lights, unless it is shorting somewhere else? Don't know, just wondering out loud. Is trailer backfeeding down the ground perhaps?

Steve

To the OP, that charge line on your Ford should be oem, and hit only with the key on. Can you verify that with a test light checking the top right pin of the 7 way?

I think it has to be feeding from the truck somehow. Otherwise the trailer would do it regardless of being hooked to truck, unless the batteries are dead and when plugged in they get power from the charge line.

Unusual....