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"dancing" Voltage gauge

1970Custom

They call me Spuds
14,107
447
Middleton, ID
Driving my pop's '96 F-250 today and noticed the voltage gauge dancing to the idle of the truck. It just, as of three weeks ago, had the entire under hood wiring replaced because of a short that ended up melting every wire and all the glow plugs. is it the voltage regulator causing this, or??
 

Skandocious

Post Whores Make Me Sick
19,076
655
California
Glow plugs? Don't know much about diesels... But this sounds like a charging system issue. Could be the voltage regulator I suppose but my first suspicion is the alternator. Does the voltage move around a lot when activating and deactivating accessories like the headlights and ac/heater? Autozone (and Kragen I think) will load test your alternator for free, although the test is not always a sure fire way to deduce the health of an alternator (ie, a tested good alternator can still be bad).
 

Skandocious

Post Whores Make Me Sick
19,076
655
California
Hmph... I'd grab a repair manual and see what it calls for as a reading from the voltage regulator and throw a multimeter on her. Sounds like it could very well be the vr... Just doesn't make sense to me for a diesel's voltage to surge with RPMs if you aren't running accessories, because it doesn't require a spark to fire like a gasser does... [confused]
 

6L PWR

Kansas Chapter member
That thar is custom!! Guys pay money to make that happen!!

I got no clue either. Hopefully one of the techs will see this soon!
 

1970Custom

They call me Spuds
14,107
447
Middleton, ID
its weird, it starts out just above the N of normal then jumps to the R after about a minute and about a minute after that it jumps to the AL and it'll bounce back and forth about an 1/8" at idle then like I said as you accelerate it'll get faster and faster and barely move back and forth, HOWEVER as soon as I get to 70 and set the cruise, or just hold it there, it'll go back to the 1/8" sweep.
 
double-check the connection at the alternator, make sure they are tight. Also, on the 96's there is a wire connection just front of the radiator support with a black connector; these are known to corrode and cause guage or idiot lights to "dance". Clean the connection really well and put it back together with a dab of dielectric compound in there.
 

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