Repairing Auto Electronics
Q. I work in an automotive garage. A car came in one day with an electrical problem; a fuse kept popping. My supervisor put a pair of needle-nose pliers into the fuse slot. When the smoke from the wires came out of the car he said, “There is the short.” It took days of replacing burned wire inside the car what a mess! I wouldn’t want to own it. When a fuse does blow is there a reasonable way to or trace it?
A. One thing you can do is solder a couple of wires to a single filament tail light. Then connect the tail light across the empty fuse receptacle. If the short exists the lamp will light. The lamp will limit the current to about one Amp, which will not harm the wires in the harness. Since any current-carrying conductor produces a magnetic field, you can sometimes use a compass to trace the wire through body panels, etc. One amp of current should give a strong enough magnetic field.
There are also pulse generators called “buzz boxes” that can be used to trace wires through bundles and harnesses. The buzz box produces pulses coming at an audible frequency. A detector consisting of a pickup loop, audio amplifier, and speaker or headphones is used to "sniff" or trace out the wire. When you’re on the wire itself you’ll hear a loud tone. If you’re farther away or on another wire, you’ll hear a fainter tone. Telephone techs have used these for years.
One word of caution is in order, though. First, don’t try to use an auto buzz box on AC power lines. Secondly, other devices are often called “buzz boxes,” too. For example, l2VDC-to-120VAC inverters are often called “buzz boxes,” too. If you decide to buy one, make sure that the person you buy it from understands what you want.