Unique Leads Find Wiring Problems That Evade Meters

By Larry Stewart | September 28, 2010


Pushing the TESlite button completes a circuit and imposes a load so the voltmeter can detect voltage drop. The test is impossible to do with normal voltmeter leads, but it measures real circuit performance better than static voltage or resistance testing.

Eighty-five percent of electrical-system faults occur in wiring, and Dan Sullivan invented a special set of voltmeter leads to make sure technicians don't overlook them. TESlite leads allow the user to read voltage drop in a circuit with the component removed. Sullivan and TESlite users say the dynamic test is a significantly more accurate way to make sure adequate current can flow than using the ohmmeter to check resistance, and faster and less destructive than reading voltage drop by poking holes in the wire's insulation with a test light.

On a service call late last year, Herbert Eggleston, mechanic at Cummins Atlantic in Richmond, Va., was getting normal readings from his ohmmeter. Components checked out OK in the truck's faulty system, too. Another mechanic tossed a set of TESlite leads to him and said, "Try these."

"TESlites actually put a load on the wire, and showed a voltage drop across the circuit," Eggleston says. "If you know you have a voltage drop, you know there's resistance in the circuit and you can get to work finding it."

Resistance fools voltmeters used in open circuits because some flow nearly always gets through, like the trickle of water downstream from a kink in a garden hose. If you close the nozzle on the end of the hose and wait, the trickle will eventually equalize pressure downstream from the kink with the working pressure upstream.

Voltage is electrical pressure. When you pull a component out of a circuit, you effectively cap the wire. Touch a voltmeter lead to the positive wire and the meter will read normal system voltage even if a corroded connector or wire upstream is pinching off current. Pressures on either side of the resistance equalize, but there's not enough flow to run the component properly—just as there won't be enough water to rinse the soap off your Corvette when someone squeezes a kink in the garden hose.

TESlite leads are simple devices that can be used with any voltmeter. They're the only leads Eggleston carries. He says they work fine for testing current and resistance.

"It speeds up the process of testing circuits because it shortens the steps you have to take to eliminate possible problems," he says. "Now I go straight to load testing the wires, because most problems are with connections. Depending on what the meter tells you, the leads can cut a three- or four-hour troubleshooting job down to two hours or less."

Sullivan says TESlite's primary benefit for accomplished mechanics allows them to thoroughly test virtually the entire length of any circuit from the location of the load component. Pull the component that is not performing properly, he recommends. Put the black TESlite lead on the negative terminal and red on the positive terminal and turn the circuit on. If the voltage reading fluctuates wildly, the circuit is open somewhere.

If the voltage is normal, push the TESlite button and watch the meter. If the reading doesn't change, the circuit is OK. If voltage drops when the button is pressed, there is high resistance in the circuit.

"You still have to take the circuit apart to find the corroded connections, but there's no doubt when you have to start looking," says Eggleston.

Sullivan received a patent for TESlite in March and he produced about 500 units last summer to sell with his electrical-system training program. At press time he had begun discussions with potential buyers of the patent who could manufacture the product on a larger scale.

TESlites are currently priced less than $40 each. For more information about the product, or Sullivan's troubleshooter training program, check out his website at www.brighterideas.com or call him toll-free at 877-WRENCH2.