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I have a 89 gmc p/u tail / brake lights not working. But ft park lights work. Licence plate light not working also
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Hi,
If you have a DMM (Digital Multimeter) you can use the Voltmeter function to prove if there is power coming to the lamps. DMMs can be purchased from most big hardware stores for as little as $10
Remove a tail lamp from its' socket and connect one lead of the Voltmeter (20V DC scale) to the chassis of the vehicle (make sure that it is a clean connection point) and then with the tail lamps switched on use the other lead of the Voltmeter to connect to the lamp connector inside the socket (from the front where the lamp connects to it). If there is a reading on the meter (should be around 12V) and if the lamp itself is OK you most probably have a faulty earth connection to the lamp assembly.
On a lot of vehicles the rear light assemblies (brake/tail/turn) share the same earth connection to the chassis through the wiring harness.
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ken foster , Just to add to jayeff good answer, if your truck is equipped with trailer light harness check or remove he harness as they can cause a lot of tail light issues when they go bad, especially the ones with converter. Good luck.
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