PUP lights and electric brakes not working

I carry one of these trailer connector 7-way test adapters (AMAZON) that really helps me determine where the problem might be at. The Truck side or the Trailer side.


My Ford F150 truck has all of those trailer wires protected with separate fuses.

I always squirt some WD-40 into the Truck side 7-way Connector and move the trailer plug connector around good a couple of times and this seems to help my intermittent operations of safety lines.

About the only thing common to all of the lights and electric brake operation going out would be the COMMON GROUND coming from the truck side.

I found my 7-way cable completely cut through on one trip one time as well. Something got caught up in a tight turn when camping off the beaten path one time... That was obvious and found real quick however...

Roy Ken

I ended up,replacing the connectors and all is working fine. Thanks for the replies!

As mentioned previously, clean the contacts on both the tow vehicle and the trailer cable. If that doesn't fix it, then the wire terminations inside trailer's plug. There probably is a small set screw on one side of the housing, remove it and slide the outer housing back along the cable toward the trailer. Check to see that the wire terminations are all clean and tight. A flat blade screwdriver should be all you need. Replace the outer housing and replace the set screw.

I had an issue with faulty tail lights that was caused by a lose ground wire connection inside the plug. 5 minutes is all it took to solve it.

One thing coming to both issues could be a bad ground.

Same thing happened here - Brodie's right. After sitting idle for the winter, the lights on my PUP were erratic. I took the adapter in on the bench and applied copious amounts of WD 40, cleaned the contacts with a wire-brush Dremel tool, then realigned everything with the smallest needle-nose I had in the shop. Lit up like a Christmas Tree! :)

I found that if my equipment was not used on a regular basis that the pins and sockets in the trailer light connector would oxidize and interfere with the lights operation.

Wiggle the connectors, use a contact cleaner, and possibly a light oil to clean and restore operation.