Trailer running lights

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Mar 1, 2011 | 05:52 PM

whitewhale

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Joined: Mar 2004

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From: Illinois

Trailer running lights

Gremlin in my dads truck('03 250 6.0L reg long bed). Running lights don't work on the trailer. Checked for power at every connection I could easily find. No power going back. Fuse is fine(#38 IIRC), I have power at the fuse. Wondering if someone knew what wire I need to probe closer to the fuse box or if there is another fuse to check? No elec. brakes either but I'm going to fight one battle at a time. Thanks in advance, Mike

Mar 1, 2011 | 05:55 PM

whitewhale

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From: Illinois

Running lights on truck work fine, it's just the trailer ones don't

Mar 1, 2011 | 10:10 PM

Benchwrench

Fleet Mechanic

Joined: Jan 2007

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From: Circle City

check for a switch, alot of truck guys will wire the trailer running lights on a "courtesy" switch.
This is how I like my truck wired too. When on the road, it's the truckin' thing to flip the trailer lights a couple times after passing and getting flashed to acknowledge it's safe to go back in the lane.

Mar 2, 2011 | 06:35 AM

whitewhale

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From: Illinois

No switch, he's had the truck since it was brand new. Everything is stock on this truck. He had to replace the RV plug once(backed into a snow bank), got a replacement directly from Ford.

Mar 2, 2011 | 09:34 AM

BPofMD

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From: Millersville, MD

How about the relay ?

Mar 2, 2011 | 09:53 AM

teppler

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From: Denison, Tx

Have you tried checking voltage at plug? Google "7 wire RV plug diagram" for diagram..

Mar 3, 2011 | 02:21 AM

Cowboy65

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From: Smiths Grove, KY

According to the electrical schematic fuse #38 feeds two relays in the power distribution box (located under the hood): 1) trailer back-up lights & 2) trailer marker lights. I would start by making sure that power is getting to the marker lights relay and that it is functioning properly. If the relay is working OK then start tracing the wiring going to the trailer plug (brown/white).

The following link will provide you with a PDF of the electrical schematic.

https://www.fleet.ford.com/truckbbas...bb_pdf/203.pdf