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Q: Turn signal, interior lights, headlights, brake lights, all malfunctioning. new bulbs, new switches

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Right interior turn signal light stays on when truck is on. if you press the cargo dome light 4 times the light goes off however after that, whenever you signal right all interior lights flash with the turn signal.

A: Thanks for writing in about your 2000 GMC S...

Thanks for writing in about your 2000 GMC Sierra 1500. Symptoms like these can be very confusing. It can almost seem like there is a ghost in the system. As simple as it may sound, you most likely have a bad ground. Keep in mind, there are grounds located in random places all over your truck. This ground likely supplies a ground to numerous lighting circuits. When there is a bad ground, or a short to power, your lighting is forced to find another path to flow. How this happens is excessively random and unpredictable. There could be a short to power somewhere as well, but bad grounds are much more common.

Finding such a problem is very difficult at times. I would probably start with the right turn signal light. Figure out why it is always on. There is clearly a short to ground or power somewhere in this circuit. Keep the diagnostic process simple. At the beginning the question is whether or not there are multiple problems or just one. Often times, diagnosing why the turn signal is always on will lead you to the source of all the problems.

The important thing to remember is that if the diagnostic path you begin doesn’t seem to have an end, start over from the beginning from a different angle. You should be using a test light and a factory wiring diagram. It should be said, a diagnosis such as this is not for the faint of heart. It is very easy to become confused.

A few common failure components include a combination switch, headlight switch and connector, damaged wiring in the steering column, and connections at the exterior lights. If you need help having this checked, I recommend having a qualified technician, such as one from YourMechanic, inspect your lights to pinpoint and correct any faults within the system.

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