Voltmeter Gauge Fluctuates Eratically

[TACO626]

Happens when I turn on headlights or push on window switches.

I did my research and did not find what I was looking for.

Thanks in advance for all replies!

 

[79broncojosh]

my 95 does the same thing, as a matter of fact every ford I own does it. I think there gauges are just really sensitive.

 

[Blacksheep Josh]

I would suggest:
1. Checking wires for corrosion, including but not limited to: Ground wires, alternator wiring loom, battery cables.
2. Check battery connections, make sure everything is tight and corrosion is cleaned away.
3. Check fuse for alternator in the underhood fuse box and also check the fusible link connected to the alternator harness.
4. If all else fails, I'd remove the alternator and have it bench tested, might also want to test the battery while you're at it.

Good Luck.

Edit:
I will say, when I press the window up switch, when the window is all the way up and I press the switch it will drop the gauge, but only because there's a serious load and the motor is working hard. But it's always done that, but if you're just idling or driving and the headlights make it dim, something else is going on.

 

[backfrmcolorado]

same problem

yeah my 94 does the same thing. it has a brand new duralast gold battery with 850 cold crankin amps and its now on a second alt. i can pull to a stop light and the engine is at about 550 rpms and everything dims. i havent been able to figure it out either and my altternator is new. the only thing that did help is to like the other guys said was to change yur fuses keep terminal clean and i also added a couple extra ground wires on the truck... frame to body, engine to frame and engine to firewall. it doesnt do it to bad now. i dont really worry to much about is tho, if the meter goes back to normal you should be good. maybe a bad batery. autozone does free checks on batts and alts. get em checked out if it gets to bad and you are worried about it.

 

[79broncojosh]

I have a brand new red top optima, new battery cables, and a custom rebuilt alternator able to produce 150 amps and mine still does it with the high load items.

 

[grant00]

could it be because of the same thing the gas gauge has? I dont remember exactly what its called but it slows down the movement of the gauge like with the fuel level gauge so you dont get readings while the gas is sloshing around in the gas tank...

 

[TACO626]

Should have an update in the morning

 

[Opera House]

If you put a meter directly on the battery it would probably be rock solid. That is because the battery and the alternator are a system tied together. The voltmeter in the cab measures voltage from the battery to the vehicle BODY. The voltage drop you see is due to poor connection from the battery - to the vehicle body as the result of corrosion. Add a new ground wire from battery - to the body.

 

[Verno]

If you put a meter directly on the battery it would probably be rock solid. That is because the battery and the alternator are a system tied together. The voltmeter in the cab measures voltage from the battery to the vehicle BODY. The voltage drop you see is due to poor connection from the battery - to the vehicle body as the result of corrosion. Add a new ground wire from battery - to the body.

Exactly what I was gonna say! Check your ground connections.