6066gmcguy has great info on testing for lighting troubles:
http://www.6066gmcguy.org/headlight.htm and
http://www.6066gmcguy.org/Electrical-01.htm

The are some testing basics that I think I need to learn before I can really use his info... He describes testing for 12 volts at the headlight switch with the switch on and getting12 v. at a certain post on the switch. How do we phyisically get the probes in there? Is this where I would use a pin stuck through the wire's insulation?


REQUIRED READING: Truck, by John Jerome
(aka "The Book of Truck")
Zen Trucking