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Blinkers flash fine while driving but not flashing at idle.

(1990 Chevrolet S10)
in Anaconda, MT on March 10, 2013
1989 S10 base model 2wd. The blinkers were working sporadically before purchase. (i.e.- not always flashing, sometimes one or the other worked fine, etc.) I replaced and/or tested the fuses and bulbs, and also the flasher, checked all grounds as well. Not sure where else to look. It had a bad alternator and battery when I purchased, so I replaced both along with the serpentine. A former owner installed an aftermarket stereo (which works and tests fine). I was hoping the blinker issue would resolve with the new parts, but just got a bit stranger instead. Any ideas?
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on March 10, 2013
Test alternator output @ idle and at 2,000 rpm. With lights on hi beam, heater on and brake pedal down. Should not drop below 13 volts and not over 14.75. Alternator may assist flasher at speed but not at idle. Try another flasher, standard duty, to see if that helps! (MAYBE)
Possible lazy alternator regulator. Will flasher work with everything else turned off but key on? One more thing, just above the park brake pedal, released, under dash is a bolt that grounds the dash unit, it takes a 10 mm socket make SURE it is tight!!! If not, all kinds of weard stuff happens with the dash and electrical system! VERY common on this year model. Other symptoms include erratic gauges,if equiped, flickering lights amoung others.

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on March 16, 2013
Ok, we tested the alt, starter, battery and all the fuses. All test fine. So, I pulled the new flasher and put in another, and now they are working again with no glitch. I feel like a moron since this seems to have been the problem even though I had already changed it, lol. Thank you so much for the very helpful advice! I can use it in the future as well!
on March 16, 2013
We try!! Also go ahead and tighten that bolt under the dash.
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