Circuit Tester

You can use an old car buzzer or any 12 volt buzzer, a circuit breaker from an old fuse block, and some wire to make a fail proof shorted circuit tester. Here's how. You wire the buzzer and the circuit breaker together terminal to terminal. Both should have only two terminals. Some car buzzers have more than two. In that case, find the two that sets off the buzzer. With the two wired together splice into each wire separately with a single wire. This should give you two separate open leads. These are the two you plug into the fuse block in place of the blown fuse. Polarity does not matter in this case. When the short to ground is present the breaker will open the circuit and the supply side of the circuit will supply + voltage and the load side which is shorted will supply - voltage causing the buzzer to sound. When the short is present you can then do a wiggle test and listen for the buzzer to stop.  Here is a picture of one below.