What is the Best Way to Check to See if a Relay is Bad on a 2008 Ford F-250

Question:

All connections worked and then hooked a friends boat trailer. When I connected the four way I heard a pop and the running lights no lnger work. have checked all fues under hood and in cab and all are good. How do I check relays

asked by: Warren

Expert Reply:

The easiest way to check a relay is to pull the relay and then insert a new one. I would say that it is likely a relay issue since you stated you checked all the fuses already. Use the vehicle owners manual to find the locations of the relays related to the tow package wiring. Before you change out a relay and reconnect the trailer you will want to be sure to determine what caused the problem in the first place.

A short on the trailer could have caused this issue and unless it is fixed it will keep happening. Start by checking the vehicle and trailer side connectors and clean off any dirt and corrosion. Then on the trailer make sure that the main trailer connector ground and the grounds for all of the lights are attached to clean and corrosion free bare metal surfaces.

Then trace each trailer wiring from the front to the back and look for any exposed wire that could be touching the metal trailer frame. I have included a link to our wiring FAQ for you.

expert reply by: Michael H