Winning tip: Staying intact

Jan. 1, 2020
Joe Glassford is this month's Mitchell 1 Tech Tip winner. His tip helps you avoid damaging electrical circuits when you test them.
Mitchell 1 tech tips automotive aftermarket vehicle repair tips technician tips You want to measure a voltage signal in a circuit you're troubleshooting but can't decide whether to back probe the connector or pierce the insulation. Piercing could damage the wire and invite corrosion, and back probing can damage the connector or worse. This month's Tech Tip winner is Joe Glassford of Sunriver, Ore., with this tip on accessing a signal without doing either.
"It is becoming somewhat difficult to determine if an area to be back probed contains a resistor that could be damaged by the back probing T-pin or acupuncture probe. An example would be the Honda 5-wire air fuel sensor. To avoid damaging these resistors or the connectors themselves, and to avoid piercing delicate wires that could lead to future failure, I recommend a procedure I call the 'hairline test tap.'

"It is nothing more than separating a single strand from a piece of wire while keeping all the remaining strands intact. Depending on how many total strands there are, the thickness of an individual strand can be as little as 0.0025 thousands of an inch. I take the separated single strand and insert it into the female end of the wiring connector I want to access. I then fold it back on the connector and hold the wire in place with tape. Next, I reconnect the connector to the harness. I now have a test lead that I can connect to my multimeter or scope."

Joe Glassford Joe Glassford is the owner of, a website devoted to voltage drop testing techniques. He retired after 29 years of service in the public school system teaching automotive repair, but remains active sharing his knowledge at events like ATE and VISION HiTech. He also is an AutoPro Workshop member, going by the screen name Vestedjoe.

For his winning tip, Joe receives a fender cover from Mitchell 1 along with a hand-crank emergency flashlight. Enter your tips at for your chance to win.

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