1988 2.9 Electrical Issue?

[88ranger91]

Watch the video I took on YouTube and tell me what you think. Only does it when cold and used to only do it for a few seconds on first cold start up of the day but I’ve found this winter even after a few minutes of driving when I come to a stop with the lights on and fan blowing hot air it will jump just like this. Battery is strong at 12.6 and alternator is at 14+. Any ideas??? Thanks guys!

https://youtu.be/UDqZo6LXjNs

 

[RonD]

So you are wondering why the Tach moves with voltage changes?


Clean Battery cable connection on Starter Relay(solenoid), remove all the wires there clean them and reinstall.

On the back of the drivers side head is the GROUND for the cab electrics, a ground strap, bolted to the head and the fire wall
Make sure it is there, and make sure it's connections are clean.


And it could be the alternator leaking AC voltage, called Ripple Voltage
Start engine
Set Meter to AC Volts
Black probe to Ground, alternators case is good
Red probe to B+, stud terminal on the back of alternator
Should show .5vAC or less, more than that and you have failing diodes in the alternator