I have a 1998 GMC Sonoma that has no heat and the blower mower hums. I have changed the relay switch and the resister. Also the third brake light comes on the the heat setting is on 3.

Asked by Feb 16, 2014 at 05:51 PM about the 1998 GMC Sonoma 2 Dr SLS Sport Standard Cab LB

Question type: Maintenance & Repair

2 Answers

79,125

Sounds like the blower motor is bad. Since it hums we know it's getting power. I'd replace the blower motor. As for the 3rd brake light, that's a new one on me. I'd have to say someone wired it in to get it to work. Just so happens they picked the wire for speed 3 on the blower switch. HTH. -Jim

The blower motor is good, the relay and resister are both new. The humming comes out of the relay on speed 1,2, and 3 the only thing that occurs on speed 4 is the 3rd brake light comes on.

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