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Edward, ASE Certified Technician
Category: Ford
Satisfied Customers: 3077
Experience:  ASE certified. Auto Transmission rebuilder for Ford Motor Co. from 91 to 2000
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Have a Ford F-150 2005. My boat trailer tail lights do not

Customer Question

Customer: Have a Ford F-150 2005. My boat trailer tail lights do not come on but flasher and brake lights are OK. Wiring looks OK, connections cleaned without correcting problem. Could this be a fuse issue? My name: Gayle Brewer, Longbranch, Washington. Thanks
JA: Thanks. Can you give me any more details about your issue?
Customer: Lights worked OK in past, now this new problem. Trailer wire connector is standard flat 4-plug type.
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Submitted: 1 year ago.
Category: Ford
Expert:  Edward replied 1 year ago.

Hello, Eddie here and I will try to help. It very well could be a fuse issue, there are a few fuses on the central junction box that need checking first. Do you know where the interior fuse panel is on the passenger side up under the dash?

Customer: replied 1 year ago.
Expert:  Edward replied 1 year ago.

Alright, do you have the owners manual in the truck by chance?

Customer: replied 1 year ago.
have manual.
Expert:  Edward replied 1 year ago.

alright, page 227 gives you a breakdown of the interior fuse panel and the fuse numbers, I would like for you to check fuse number 10, it is a yellow 20 amp fuse, that powers the trailer park lamp relay, and if that fuse is good, I want to swap the relay next. Are you working on it now?

Expert:  Edward replied 1 year ago.

Let me know if you find anything there with the fuse, the parking lights work on the truck correct?

Customer: replied 1 year ago.
Not working on it now, will have to wait until tomorrow AM.
Expert:  Edward replied 1 year ago.

No problem, We can try it in the AM. Thank you.

Customer: replied 1 year ago.
Park lights work OK. Fuse #10 is good, not blown. What to do next?
Expert:  Edward replied 1 year ago.

Hello, can you swap that trailer lamp relay? Im thinking its position 201, but Im only on cell service right now, you have the owners manual and looking at the diagram of the interior fuse panel?

Customer: replied 1 year ago.
in truck looking at fuse panel and diagram. there is a #201 relay. Don't know what is meant by swapping relay?
Expert:  Edward replied 1 year ago.

look at the delay relay, swap it if it is identical, should be a part number on the trailer tow lamp relay, I want you to swap it with an identical relay in the fuse panel if possible, your sure this trailer isnt the issue right? Could you plug it into another truck just to be sure the running lights do work?

Customer: replied 1 year ago.
Don't think trailer wiring is problem (checked that first) but not 100% sure. Will see if a neighbor can hook up his vehicle to trailer to test that out before going further with truck electronics. Will let you know if need more help with truck. Cheers.
Expert:  Edward replied 1 year ago.

Sounds good, let me know what happens. thanks, ill be home later and I can pull the wiring diagram if needed.

Expert:  Edward replied 1 year ago.

I'm back home now. Any luck with it?

Customer: replied 1 year ago.
Good timing. Neighbor Larry just hooked his vehicle up to trailer and trailer lights are all OK. He used his tester to confirm low but present voltage to park/trailer light channel of truck light hitch, and good voltage to brake and flasher channels. Doesn't think this is a fuse problem. Thinks problem is most likely in wire connection to truck light hitch socket, which I will work on if I can get truck to a dry spot to work on (raining non-stop here). Big thing is that trailer OK; sold boat and new owner picking up in a few days.
Expert:  Edward replied 1 year ago.

Alright, good deal, so the problem is in the truck, Swap that trailer running lamp relay in the interior fuse box with another one if you can, and if that isn't it, be sure check all the fuses out under the hood as well. Test light works well for testing them you can just touch each side of the fuse blade and if the light comes on, you know the fuse is good. I believe you'll find your problem either in the running light relay, or that connection between hitch socket and trailer. Let me know if you have any further questions. Thank you.