Hi KJ88,
The speedometer jumping around could be due to a faulty speed sensor located on the trans axle differential housing below the thermostat housing. It could also be related to the lights flickering and I would suggest rectifying the the lights flickering first.
Possible causes are:
1. Bad body ground. Check all grounds at front fender inner side behind headlights.
2. Alternator. Check the charging rate, ensure crankshaft pulley harmonic balancer is not faulty ( if equipped) before testing charging rate.
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Wednesday, April 7th, 2021 AT 12:56 PM