Originally Posted by smokeywren

One way is as explained in my previous post: "You need to use a 7-pin plug tester and test the 7-pin plug on the back of the pickup with the tranny in reverse. If the center pin is not "hot", then you must add a fused wire to the wiring harness, to bring 12-volt battery power to that pin. Here's one example of a 7-pin plug tester:
http://www.etrailer.com/Wiring/Reese/78118.html "

Of course, the engine should be running and someone's foot on the service brake when that someone puts the tranny in reverse while you are observing the tester lights.

Originally Posted by spotterjoe

That Reese adapter that you listed will not test the center conductor. It only tests the 4 way side, not the other pins.