Check out some similar questions!

Dr D · Nov 11, 2006, 08:32 AM

As we know, you can do a continuity test on automotive wiring that shows good, but due to a high resistance connection, it won't carry a load. Some months ago on one of the car shows on Speed Channel, they touted a neat tool (about $100) that can put a load on the wiring circuit to locate the problem. Does anyone remember the name of the company that makes it. I have a buddy who hooked up 110 volts to the wiring for his Camaro tail lights, and looked for smoke or fire at the bad connection. This is obviously not a good way to locate the problem. By the way he did locate the bad joint without torching his car or killing himself. Thank you for any help

TxGreaseMonkey · Nov 11, 2006, 09:08 AM

Dr D, if you disconnect the negative. Terminal of the battery, you can safely use an ordinary digital multimeter on your car to test for resistance (ohms) and not just continuity. Similarly, if you know the input voltage on a circuit, you can set your DMM to DCV and check for voltage drop. I would recommend a Fluke 16, which can be used on automotive and HVAC applications. Besides all normal capabilities, it allows you to test capacitors, diodes, and, with the use of an included thermocouple, temperature.

Dr D · Nov 11, 2006, 11:18 AM

Dear txgreasmonkey, I thank you for your response. I assume that the voltage to the lights is 12 V. If one put the VOM at the terminus of the circuit, by the tail light socket and the other lead to ground, how much of a voltage drop would indicate a high resistance joint? Since the meter doesn't apply much load, wouldn't the drop be greater with a bulb demanding power? As for resistance in the wire from front to back, I would think the ohms should be close to zero for a good wire. What ohm reading do you think would indicate a less than good connection. Thanks again.

TxGreaseMonkey · Nov 11, 2006, 11:42 AM

The voltage drop should be nil on a good connector. Just make sure the black test lead is pressed firmly into a good, clean ground. The voltage going to the connector is not going to be affected by whether a bulb is installed. It's difficult for me to answer your last question precisely. For reference purposes, check the resistance (ohms) of the other good tail light.

As you know, most people troubleshoot tail light issues with a simple test light. The basic issue is whether you are getting power or not. It's normally a yes or no situation. Precise voltage and resistance measurements usually aren't made. If necessary, a test light or DMM can help locate an "open" in the circuit. A quality test light glows more brightly with higher voltage, which helps you assess circuit resistance, not just continuity. Hope this helps, even though I haven't seen the tool mentioned on the Speed Channel.