Trying to diagnose the AC controls on my car. Took the unit out and came across a transistor that read faulty after removing from the circuit. From the research I've done, I'm to believe it's an NPN transistor as that's how it tested. Got a TIP31AG transistor from radioshack. Appears to work, but I don't get the 12v from the transistor that is needed. Any help would be greatly appreciated.