Left turn signal flashing rapidly

THERUSSELLS1998

MEMBER
2000 GMC SONOMA
6 CYL
4WD
AUTOMATIC
87,000 MILES

Left turn signal flashes rapidly, replaced flasher unit and all bulbs. With no change. Also have checked fuses in the fuse panel on the drivers door side on the console. All the bulbs have been replaced and working correctly, except for the rapid blinking.

Hazard flashers are working fine as well.
Switched bulbs from left to right, again all still working correctly, left side still blinks rapidly.

Lights that have been checked are headlights, tail lights, park lights, turn signals, hazard lights, backup lights have been checked and verified working, unless there is a secret light that has not been checked.

8 Replies

FACTORYJACK

MECHANIC
4,159 POSTS

If all the lights function normally, I would suspect that there is high resistance in the left side circuit somewhere. The trick is going to be isolating it. For starters, does the vehicle have some sort of trailer wiring? Next would be to look for something that may not be too obvious, but may give a sign. Is there any difference in bulb intensity (brightness)? You could have a socket with a bad ground and it is feeding back through another circuit. I cannot say as though I have seen a vehicle with a rapid flash on one side, and all lights functioned normal. There is no service procedure for that symptom in the service manual. When did this occur, or when was it noticed?

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Sunday, June 27th, 2010 AT 3:38 PM

THERUSSELLS1998

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2 POSTS

It started happening shortly after we bought the truck, used. We put in the new flasher unit, and the flashing increased, which we both thought was weird.

There is trailer wiring I do not know if he has checked that out yet, but he is usually thorough, although this has him really frustrated.

We have a manual with the electrical sycamatic in it.

Hubby is electrical engineer for most part, and has tried everything that he can think of short of pulling the wiring in the truck with a voltage meter. Will tell him what you have suggest, he said that he had been in the truck, under the truck, under the dashboard, almost inside the glove box.

Could the unit that the flasher is plugged into be having an electrical issue?

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Sunday, June 27th, 2010 AT 3:51 PM

FACTORYJACK

MECHANIC
4,159 POSTS

You would think if it was as central as the flasher, you would have issues on both right and left. If they were both flashing fast, it would almost seem normal. If the trailer wiring is not factory, it might be suspect.

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Sunday, June 27th, 2010 AT 4:01 PM

DEMIREW ASFAW

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I had this problem it ended up being the turn signal switch. FYI

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Tuesday, July 31st, 2018 AT 2:51 PM

KRAMPN17

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2 POSTS
2000 GMC SONOMA
4.2L
V6
2WD
AUTOMATIC
132,500 MILES

When I turn my right turn signal on it blinks at a rapid speed. When I turn my four ways on it is back to normal. I have put all new bulbs in and it still does this. I checked the fuses and they are all good. The grounds are grounded. Also my reverse lights do not come on.