[FED 387]

CHECK the wiring to make sure you have the wires in the correct position in the trailer plug in relation to the truck receptacle--- look inside the cover flap on the truck and it will give you the position number and the wire color for each position make sure it matches the trailer pattern--- some use the RV pattern and others may have used the commercial truck wiring pattern--- also if your truck is over about 10 yrs old the factory wiring receptable is probably corroded inside & you can get a replacement unit on ebay for less than $10--- my experience on this!!!!---FED 387