In The Shop: Piercing Problems
Aug 22, 2010
Electrical tech books and electronics classes tell mechanics and do-it-yourselfers (DIY) not to pierce or disrupt the insulation on electrical wiring while testing circuits. But sometimes there's no other way to accurately test circuits.
The tool industry has noted the problem of testing circuits and offers several useful tools to probe wiring. Back-probes are gadgets with thin, stiff wires that allow the user to probe into the backsides of electrical connectors to make contact and test individual wires. Back-probes come in a variety of sizes. A few come with the probing wire at a right angle to its "handle", which is handy when probing big connectors with lots of wires.
My favorite probing tool is "The Claw" by Ferrett. Hard to describe, but it's a thumb-screw gizmo that cradles the wire to be tested so a pin-point probe can be screwed through the insulation of individual wires. I like The Claw because I can test wires away from crowded plugs and leave individual Claws connected to the wire for repeated tests. The Claws come four to a package and are color-coded red, black, yellow and blue to help keep track of which probes are testing which wires. The Claw sells for between $30 and $40, depending on where you buy the kit.
There are other ways to probe and test wires, including the often painful process of simply poking the tip of a voltmeter probe through the insulation (and often into your fingertip). That works, but isn't very tidy. Whatever type of probe is used, be sure to close the small break in the insulation to prevent corrosion to the wires. I like a dab of "Liquid Insulation" a liquid plastic that seals to a rubbery finish. A couple turns of electrical tape is better than nothing.
Above all else, don't use a pocketknife to peel back an inch of insulation. Unless you want to spend a lot of time re-testing the same wire next year, after a bunch of greenish corrosion disrupts voltage and resistance in that wire.