Q: I am having a problem troubleshooting the trailer light plug on a 2002 Chevy Silverado. I get no power there. I've checked all the fuses and they're good. I expect it's a simple grounding problem, but don't know how to proceed.

A: The trailer wiring is a little different on light- and heavy-duty trucks, but the basics apply to both. No power at all to the trailer connector would mean a major break at the connector or the wiring harness. The turn signal/brake, parking, and backup light terminals at the connector receive power from different sources. Keep in mind that checking for 12 volts with a test light won't show any voltage until each circuit is turned on. For example, if you turn on the ignition and a directional, you should get a flashing test light at one of the trailer connector terminals. With the directionals, power comes from the Turn fuse under the left side of the instrument panel, then through the turn/hazard flasher (underhood), then though the directional switch, and then through left- and right-turn fuses (underhood) before leading to the trailer connector. There's only one terminal at the connector that supplies a ground. If that were bad, you'd still have power, but no ground as a return path for voltage after passing through the trailer light bulbs. Everything could be fine at the connector, while a poor ground to the frame of the trailer kills everything. Start by confirming which circuits actually have no power, or if there's a bad ground, and take it from there.

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