I own a '98 F150 with factory installed towing package. I have used it to haul a utility trailer for about two years. Two days ago, I hooked on to my trailer only to discover that the trailer lights had stopped working. The lights on my truck work perfectly normal. I found a bare wire touching the frame of the trailer and repaired it.

The only thing I could think of was a blown fuse??? I turned to my owners manual and found the fuse locations. I discovered a blown mini fuse in the Power Distribution box (20amp running lights) and replaced it. Well, this gave me tail lights on the trailer. But still No Brake or Turn signals. I checked the connection on the truck harness plug. The terminals were clean. The ground wire connection is good and clean. I removed the plastic shield from the harness and inspected for broken or frayed wires. Nothing, all looks fine.

The owners manual does not detail the relays (I think they are relays) in the little 1" X 4" rectangular box next to the Power Distribution box...... Does anyone know if any of these is associated with the trailer lighting?

In searching previous posts, I notice that this is not that uncommon an occurrence. The posts that I have reviewed however do not give explanations as to how the problem was solved. I cannot directly e-mail anyone because I have not been a member long enough and do not have enough posts. FRUSTRATING!!

Thanks for any suggestions,
Ken

p.s.
The trailer lights work perfectly when I hooked it to my other truck.

 

WhipsnHorses directed me to a third fuse box that was not mentioned in my Owners Manual. 20 amp mini fuse blown. Trailer lights operational once again. Thanks so much for the help.
Ken

 

I would recomend getting a 12 volt test light, a good one is only 10 - 15 dollars. Use it to figure out if the truck is putting power out to the plug. If not then you know the problem is in your truck, like it was said above check for the other fuse block, i am however not familiar with F-150s so I can't be any more specific for you, but the test light is very useful and will narrow down the search area. Also use the tester at the lights themselves if the truck is good

 

I have a '98 F-150 with exactly the same problem. Brand new trailer and the first time I pulled it I pinched the wiring harness on the bumper. The tail lights are on after I spliced where the harness was pinched in two but I can't get the turn signals and brake lights to work. No power at the plug and since The wires were pinched and grounded I was sure it was a fuse....where is the other fuse box? As you mentioned, it's not in the manual....need help!!!!

 

The fuse box with trailer light fuses is a small (1" X 4") plastic box on the inner fender just below the left hood hinge.

 

I just had the same thing on my Dad's 97 this week.That little fuse box is easy to overlook.

 

Now would have ever thunk it to look there. What a ducky good idea to place one there.

John

 

Great....I found it and just as expected the 20 amp fuse was blown....thanks to all for your help.!!