Trailer lights
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Senior User
Joined: May 2011
Posts: 296
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From: Rockland co. N.Y.
Trailer lights
I can't get my running lights to work on my trailer. I checked the plugs at the rear of the truck for the trailer hook up with a test light and I have power for everything except the running lights. Does anyone have any idea what it could be. I am going on a trip tomorrow and would like to try and get them working before. Thanks in advance
is a BAAAD MAN
Joined: Apr 2005
Posts: 3,738
Likes: 5
From: Winston Salem NC
I have problems with the pigtail behind the plug on the truck. I have to wiggle it sometimes to get everything to work. I clean it and grease it every once in a while but it still gives me problems.
Elder User
Joined: May 2005
Posts: 581
Likes: 1
From: Montana
sorry to butt in on your thread but i am having the same problem. mine is a 03 f 350 4 wd, 7.3. bought a boat and trailer hooked it up and the tail lights stopped working. unhooked trailer. was completely wired wrong but i cannot find a fuse or anything to get the tail lamps working again. fuse box is under the stearing wheel. no indication in the book which fuse it is, tested everything in the fuse box. any help would be greatly appreciated.
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Elder User
Joined: Sep 2011
Posts: 979
Likes: 4
From: Vancouver
The fuse box is not inside the cab. All fuses for the engine and running, signal, stop lights are in the under hood box.
The trailer light and trailer battery charging relays are attached to the under hood fuse box. There are separate fuses which feed power to those relays. If connecting the trailer lights turns off the lights, there is a short in the trailer wiring, not in the truck wiring. Use a multimeter to check resistance to ground on the trailer for each power wire going to the trailer if you do not know which wire feeds the lighting. Before doing this, disconnect the trailer pigtail from the truck receptacle. It should not be close to zero ohms in the resistance mode. Trailer wiring can be difficult.
Another cause of no trailer lights-a bad ground. Find the ground connection for the pigtail, it will be close to the hitch. Remove and clean any corrosion, apply a small amount of light grease or Vaseline, use un-rusted bolt to reattach the ground wire. Look also for bad/corroded splices in the pigtail to trailer wiring for the lighting circuit. Larry
The trailer light and trailer battery charging relays are attached to the under hood fuse box. There are separate fuses which feed power to those relays. If connecting the trailer lights turns off the lights, there is a short in the trailer wiring, not in the truck wiring. Use a multimeter to check resistance to ground on the trailer for each power wire going to the trailer if you do not know which wire feeds the lighting. Before doing this, disconnect the trailer pigtail from the truck receptacle. It should not be close to zero ohms in the resistance mode. Trailer wiring can be difficult.
Another cause of no trailer lights-a bad ground. Find the ground connection for the pigtail, it will be close to the hitch. Remove and clean any corrosion, apply a small amount of light grease or Vaseline, use un-rusted bolt to reattach the ground wire. Look also for bad/corroded splices in the pigtail to trailer wiring for the lighting circuit. Larry
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Elder User
Joined: May 2005
Posts: 581
Likes: 1
From: Montana
for future reference, my 03 superduty has two small boxes under the hood behind the air cleaner. one box has ( 2) FOAB-14B192AA in it and the other has (1) FOAB-14B192AA and (2) F57B-14B192-AA in it. the rest is under the dash to the left of the stearing wheel. 48 fuses, 10 relays,and 16 larger fuses the you can see into. dont know what they are called. i have tested all of them at lest 4 times already. i'm thinkin there may be a relay tripped somewhere . if in fact there is one. dutch
Post Fiend
Joined: Mar 2007
Posts: 26,966
Likes: 50
From: Texas
Starting in 2002, the underhood fuse box was discontinued and all fuses were moved to under the dash. There are still a couple of relays under the hood, but the (much easier to mess with under the hood fuse box for trailer lights and such) is gone.
If you need the location of fuse numbers, check your owners manual. If you don't have a manual, you can download one from Ford here Owner Manuals | fleet.ford.com
According to that downloaded manual, on page 180 it lists, fuse/relay location 38, 20 amp, Trailer tow park lamps. For the diagram of the fuse box showing fuse locations see page 178. It shows the bottom row of fuses start at fuse #48 on the bottom right hand corner, so counting 11 fuses to the left will give you fuse #38
If you need the location of fuse numbers, check your owners manual. If you don't have a manual, you can download one from Ford here Owner Manuals | fleet.ford.com
According to that downloaded manual, on page 180 it lists, fuse/relay location 38, 20 amp, Trailer tow park lamps. For the diagram of the fuse box showing fuse locations see page 178. It shows the bottom row of fuses start at fuse #48 on the bottom right hand corner, so counting 11 fuses to the left will give you fuse #38