Recheck the trailer harness and connector. In particular where the wires terminate inside the connector( on the 7 pin connector).

Which connector are you using the flat 4 pin or the round 7 pin?

The 4 pin connectors are notorious for the wires fatiguing/breaking where they are molded into the black rubber. Verify continuity through the connector.

If you are using the 7 pin do you have trailer brakes? If so check all of the brake connectors in particular where the splices are. Same for the light circuit wires. What I find is the trailer manufactuers like to use the "scotch lock" type connectors. Even the HD connectors with die electric grease inside them dont work well for long. Corrosion and incorrect installation techniques contribute to the problem(s).

Also look at the factory truck harness. Look at where the factory harness terminates into the rear of the trailer hook up sockets. Verify that the trailer towing harness is securely plugged into the chassis harness by the spare tire. Separate it and make sure no corrosion is present in the male/female connector.

All this assumes that the trailer light bulbs are good, the trailer has good grounds and that you have in fact verified the fuses feeding the brake controller and trailer light circuits have continuity(are not blown).

 

Hi
I have a 2012 F250 and my trailer turn and brake lights stopped working. I had to replace a fuse located under the hood in a black box near the firewall on the driver side. I can try to figure out the number if you need me to. I found the info in my owners manual. Hope this help you get the problem solved.

 

Thanks Eric that is some helpful information right there.

 

 

Check the in-bed trailer outlet and see if those work (use a meter or test lamp). Just because it looks neat doesn't mean that the circuits to the rear bumper's connector are still intact. With ALL trailer lamps non-functional, then the extra adapter becomes the prime suspect.

There are two separate relays ,one for each side for the trailer stop/turn lamps.. The odds of both relays failing is practically zero. There is a single fuse, F100 in the BJB, that supplies the two circuits with their operating power. Did you specifically check it to verify it is passing power? The trailer park/running lamp is fed by a different fuse/relay combination. The odds of all failing simultaneously.is even closer to zero.

The only thing the park and stop/turn signals at the trailer connector have in common is the ground. Verify it is good. Just because you have the trailer coupler on the ball never ensures you actually have a complete ground circuit.

 

I have the exact same problem, 2015 F350, TOW was working for awhile, parking lamp fuse blew, replaced, everything worked again for a bit, then all of a sudden, nothing. Looked at the tow plug assembly on ford truck, found corrosion, cleaned it up, used a tester, still no power.
Checked the fuses, replaced them. (#10, #22, #26, #90, ) I have not replaced tow relays #76 or #29. Still NO POWER. (Tested the lights on trailer, they work fine with a 12v battery)

What is the part # for the wiring assembly to replace the wiring on truck? That's the only thing I can think it is. Besides worse issues.
Thanks.

 

Check to make sure the ground wire is getting a good ground.. Most of the time electrical problems are ground related.

 

Not at all.

In any event, if he had a ground problem in the trailer lighting circuit, it would affect all of the lights, not just one function.

 

I've had a similar problem that I believe but can't confirm started when I had to jump start the truck with a trailer hooked up. Several fuses under the hood along with a relay were changed (refer to owners manual for slot numbers but 73 appeared to be the culprit) and I now have trailer lights but only when the headlight switched is taken out of the auto position. When it is in auto, the trailer lights work when the door is open. More confusion I suppose.

 

Guys. helpful i formation here but none of it is working for me. I have a new to me F550. The trailer lights worked before I replaced the plug. the trailer lights work with my 99 super duty. I have 6 amps at the plug for the running lights and 5 ish amps for the turn signals. I even plugged in a jumper setup and tested at the end of it so I am getting good contact at the plug. no lights are working on the trailer. any help is appreciated.

 

Have you tried using Forscan to reset the Trailer control module
i had same problem replaced the #26 30amp under hood then rest the module works fine now
at first i lost running light then the turn lights where out of sink then every thing went out.
thats when i went through the reset motions

 

Weird thing happened. After spending an hour testing everything I started the truck, plugged it in and went for a drive around the neighborhood. At the second turn the lights all came on and have worked fine ever since. These "smart" trucks are too smart for their own good.

 

I would suggest it isn't necessarily the 'smart' truck. It is more likely that there's an issue at the connection point - I have seen several people complaining that the new '23 plug on the truck gives a 'looser' fit on trailer plugs than 22 and previous. Likely a supplier change and inadequate testing caused this.

I've been using one of those ball-bungee cords for years on all my trucks. Plug the truck in, wiggle the connector til all lights work, then wrap the bungee around. Haven't had an issue since.