the #3 wire yellow on my truck

 

That Might be the signal wire (constant five volts) or, it might be the return wire. (should be varying voltage.... 0-5) If you are using a digital meter, it simply isn't going to react fast enough to show you what's really going on....... Wiring diagram I have is for an 01, so, wire colors don't match.

 

thanks i was

 

A test light *might* work....... you should see it blinking......