Truck Repair: F350 no head or tail lights, test light, trailer wiring

Question
We have a 2000 F350 Dually truck.  The head and tail lights are not working.  All fuses and relays are O.K.  Any suggestions as to what could be wrong?

Answer
Hi Catherine,
Make sure there is power at the fuses for the headlight curcuit, next make sure there is power at the relay for the headlights.(test with headlight switch on) you should have 2 points where there is power where the relay plugs in, if you look on the relay it has pins 85,86,30,87,and 87a. 85 and 86 are the "primary curcuit"...there should be power to one and the other will be a ground, verify both are present with a test light. If so, check for power at 30 or 87, if there is power at these said points then replace the relay. A problem area could also be trailer wiring. if your trailer has an issue it could have blown a fuse (or breaker) in the truck..make sure the trailer connector(if you have a trailer)is not connected when doing these tests. If you need more help don't hesitate to ask.

good luck,
Matt