You're two steps ahead of most people. Sounds like the switch is working, and you know the solenoid is okay. That just leaves the wiring. If you connected your drill battery to a single wire in the solenoid's electrical connector, and the other terminal to the body, that proves the solenoid's ground wire is okay too. If the solenoid has a two-wire connector, you also have to look at the ground wire in the trucks harness.
Do the same test light test right at the solenoid connector in the back. My guess is it won't work there. That means there's most likely a broken wire going back there. You'll have to follow that wire and take voltage readings at any accessible test point to see where the voltage is lost.
It is possible there is a relay involved. You can tell by looking at how beefy the switch is and the size and color of the wires to it. If there's two large diameter wires, there may not be a relay. If the wires are small and none are the same color as those in back, there probably is a relay somewhere. Relays don't fail very often. Usually you'll find a corroded ground connection to the body or a broken wire.
Also, if the test light works in back at the connector, look at how the solenoid is grounded to the body. If it's through the tail gate hinges, that will show up as the test light lighting up on both wires in the connector when it is connected to the solenoid.
Monday, February 13th, 2012 AT 10:34 AM