I have a 2012 F-350 single rear wheel, standard cab with a V-8 automatic with a little over 135,000 miles on it. I've suddenly lost the trailer running lights. I lost them once before and fixed it by replacing the fuse. ( I wondered what caused it to blow) I've had trailer running lights for a year or two since then. All the lights on the truck itself work with the exception of the right mirror marking lights. I replaced the 30 amp fuse under the hood a couple of times to no avail. The hazard, brake, and turn signals all work. Neither the running lights on the 7 pin or the 4 pin work. I replaced the connector that you plug the trailer into thinking there might be a problem there but that didn't change anything. I tested the wires coming into the truck side connector and don't have anything coming into it. I bought a Haynes repair manual yesterday but that doesn't show the trailer wiring, everything else but that. The odd thing is that I have a 7 pin test light and that shows the running lights to be working but when I hook up to either of the three trailers I have, none have running lights so I'm guessing it's not a trailer plug issue. If nothing else worked I might suspect a bad ground but everything else does work. Where does that trailer harness ground anyway? I've even thought about running a wire from an upfitter switch to the trailer running lights, (that would be the brown wire right?) but I'd really rather fix it right. I've run out of ideas. I'd take it to a dealer but finances are pretty tight right now. Anybody got a suggestion?

 

Questions , always questions.
The plug coming off the F350, are the openings flat or circular?

Utility/Equipment/Cargo trailers use one type color code - Traditional SAE

5th wheel/Travel Trailers/ Campers use a different color code- RV Standard

How about a little help here, which are we working with?

As a last resort , can you supply the wire colors in the 7 way cable coming off the F350?

Working with heavy duty tractor trailers , they were all wired the same and tests were easy and quick. The 2 above are completely different.
Thanks.

 

The7 pin connector are flat blades and the 4 pin are round. I'll have to get back to you about the wire colors. It's whatever was standard from the factory in 2012. The usage is an equipment trailer. Not 5th wheel, or camper or anything else.

 

Thanks,
The 7 way plug set up shown for equipment trailers uses the "Traditional SAE " set up.

The wires colors should be as follows,
Brown-tail lights /running lights
Red/Black- 12 volt hot lead
Purple - Reverse lights
Green - Right turn/Stop
Yellow - Left turn/stop
Blue - Brake controller
White - Ground
One of the things we learn is to VERIFY, info, to make sure there were no changes made that were not disclosed.
In spite of our best efforts sometimes things are not always as they are supposed to be , so we check and verify, OK ?

 

Thank you. I'll re check the wires when the weather warms up a bit. It's about 20° and windy at the moment and my garage is full so I'm outside working on it.

 

20 degrees ???? you must be having a heat wave , lol.