Need help finding a tow package relay
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5th Wheeling
Joined: Aug 2009
Posts: 42
Likes: 0
From: Olathe, KS
Need help finding a tow package relay
Original owner, '98 XLT Supercab, 204K miles. Factory tow package.
I finally got around to digging in to a trailer light problem, which I quickly determined was on the truck side. I found fuse 1 in the underhood power distribution box to be blown. According to the owner's manual, this fuse feeds two relays: "Trailer tow running lamp relay, Trailer tow backup lamp relay." So I assume at least one of these has welded closed, causing the fuse to blow. The problem is, I can't find these relays! I've twice gone over the relay descriptions in the owner's manual of both the power distribution box and the dash fuse/relay panel. No relays by those names are listed anywhere.
Any ideas?
Also - if anyone knows where I can get GOOD wiring diagrams for this truck, I'd love to know.
Thank you!
Mike
I finally got around to digging in to a trailer light problem, which I quickly determined was on the truck side. I found fuse 1 in the underhood power distribution box to be blown. According to the owner's manual, this fuse feeds two relays: "Trailer tow running lamp relay, Trailer tow backup lamp relay." So I assume at least one of these has welded closed, causing the fuse to blow. The problem is, I can't find these relays! I've twice gone over the relay descriptions in the owner's manual of both the power distribution box and the dash fuse/relay panel. No relays by those names are listed anywhere.
Any ideas?
Also - if anyone knows where I can get GOOD wiring diagrams for this truck, I'd love to know.
Thank you!
Mike
Hotshot
Joined: Jan 2004
Posts: 19,762
Likes: 1,079
From: St Louis
Yeah, they're not in the owner's manual for the trailer tow package for the 97 and 98s.
There's a post floating around here with an annotated photo of my old F150's "extra" relay box. I'll see if I can come across it and post a link.
It's in this thread from 2008 at sister site. Starts around post #47, photo is in post #50.
https://www.f150online.com/forums/to...locations.html
There's a post floating around here with an annotated photo of my old F150's "extra" relay box. I'll see if I can come across it and post a link.
It's in this thread from 2008 at sister site. Starts around post #47, photo is in post #50.
https://www.f150online.com/forums/to...locations.html
Thread Starter
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5th Wheeling
Joined: Aug 2009
Posts: 42
Likes: 0
From: Olathe, KS
It's in this thread from 2008 at sister site. Starts around post #47, photo is in post #50.
https://www.f150online.com/forums/to...locations.html
Thank you!!
Thread Starter
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5th Wheeling
Joined: Aug 2009
Posts: 42
Likes: 0
From: Olathe, KS
Both relays test good and all connections look clean, so now it’s a mystery why the fuse blew. 
Assuming there isn’t a short somewhere in the tow harness, the next stop is a reverse lockout solenoid in the trailer tongue. Great...
But thanks again!
Mike
Assuming there isn’t a short somewhere in the tow harness, the next stop is a reverse lockout solenoid in the trailer tongue. Great...But thanks again!
Mike
Hotshot
Joined: Jan 2004
Posts: 19,762
Likes: 1,079
From: St Louis
Most likely, it's being caused by a wiring fault on the trailer. Chafed wiring is a common problem as is water in a light that corrodes and shorts out the circuit to trailer ground (which blows the fuse under the hood) when the running or headlights are turned on.
Check the brown wire on the trailer for any short to ground.
Here's one. It's no bargain but it's what you're asking for: https://www.ebay.com/itm/1998-Ford-F...4AAOSwNXpcP028
If you can locate a used service CD/DVD for your truck on eBay, then you'd have the ETVM plus the shop manuals (on computer). Here's one: https://www.ebay.com/itm/1998-Ford-F...8AAOSwwj5b9AS3
Check the brown wire on the trailer for any short to ground.
Also - if anyone knows where I can get GOOD wiring diagrams for this truck, I'd love to know.
If you can locate a used service CD/DVD for your truck on eBay, then you'd have the ETVM plus the shop manuals (on computer). Here's one: https://www.ebay.com/itm/1998-Ford-F...8AAOSwwj5b9AS3
Thread Starter
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5th Wheeling
Joined: Aug 2009
Posts: 42
Likes: 0
From: Olathe, KS
Yes that'll be the next step. Unfortunately the trailer is 4 hours away and I won't be down there again for a couple of weeks. I looked on ebay for manuals before with no luck so I'll have to have a look at your links.
Thanks again!
Mike
Thanks again!
Mike
More Turbo
Joined: Oct 2019
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Cargo Master
Joined: Jul 2017
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good luck man! i just found a chafed wire for a side marker light on my 20 year old landscape trailer. kept blowing the running lights fuse in the f150 and my f250 on the rare occasion i swapped trucks. some goon ran the wire between the deck and the frame lol. you can pick up a new trailer wire harness cheap on amazon. might be worth a shot. replace all the wiring from the pin to the trailer taillights, if you can't find anything wrong on the truck side and the trailer wiring appears fine.
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Thread Starter
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5th Wheeling
Joined: Aug 2009
Posts: 42
Likes: 0
From: Olathe, KS
Thanks! I replaced the fuse and everything seems good at the truck’s connector now, which is sort of bad news because the boat is stored four hours away and I won’t have most of my tools, etc. With a steel boat trailer everything is inside the frame so finding anything visually is out. 99% chance it’s an intermittent short so catching it will be nearly impossible. Lights are sealed LED’s, haven’t been submerged in four years, and worked fine the last time I towed the trailer, so I don’t think it’s the fixtures themselves.
Ugh.
Ugh.
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