[Parisjet]

Paul,

Joe gave us all an excellent tutorial on what to check and why. Thanks Joe.

Another little trick that I use when checking unknown circuits or plugging in a questionable DC component is to cobble up an inline fuse holder with the about a 5 amp fuse. That way if I am plugging into a dead short, the fuse goes pop, and nothing is harmed.

 
I have a 6 ft jumper wire with alligator clips that i installed a auto reset circuit breaker in the middle. If you happen to hit a live wire or something that draws more than 10 amps it will trip and then reset after 15-30 seconds.

Recently i found re-setable circuit breakers on Amazon which are great if you have a circuit that gets blown often. (One for the bay lights comes to mind) They are $20 for a pack