The blue box you describe is a module. They do occasionally fail. Seeing you have voltage going to the switch, but not battery voltage, rules out a broken wire in the door crossover. (The wiring from the cab, through the black fexible rubber to the door) however, it doesnt prove the wiring is good either. For example, if you have 48 strands of wire that make up a single wire, if 40 are broken, then current flow wont be good. Make sense? From my experiences though, I have seen the lock module fail. They are common, and fairly cheap from a junk yard. Start here before tearing into this thing. Some techs here do stuff "by the book" im trying to save you the hassle of that. Keep in mind, if after replacing the module and its still inop, then we have some serious electrical to get into. I dont know your capabilities, but if your willing, I can try my best to help you through it.
Please consider a to help us answer more questions.
Saturday, November 2nd, 2013 AT 6:41 PM