I have a 2000 S10 PICKUP 3 doors and the left blinker statred to work real fast thought i was a burnt bulb put new bulbs in front and rear samething happening. Right side works fine took bulbs and switch them around and still left side blinks fast. Put in a new flasher still left side blinking fast any help would be appreciated

 

Howdy, alexseto. Have you replaced all the bulbs with new ones? and checked the ground wires to the chassie. There are black ground wires in the rear that are attached with 10mm bolts they could be loose.
Also check your fueses.
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I had the same issue on my 03 ... the multifunction switch stalk needs to be replaced.

 

You might also want to check the trailer harness if there is one, mine had the same problem because there was a short in the trailer harness. It didnt make much sense the way it happened, but it worled when i fixed the shorted wires so whatever.