Problem with battery gauge in my 1990 Mustang

[Higu]

It's more of an annoyance because I far as I can tell it doesn't really effect anything other than brightening or dimming the lights.

Basically, the battery gauge needle will rise or fall dramatically along the gauge. It'll start normal, then shoot up to the highest, then the next minute will fall down to where the battery light comes on. I know it's not the battery or alternator, but for the life of me I cannot figure out what it is? Loose wires or connection somewhere maybe?

[GT800]

I would say a loose or half broken wire

[jules82]

I know your system to well had that problem? Could be 3 things mice ate wires (happened to me), Reg witch is on the fender well seperate from alt or alt. You have 3 wires on your alt Sat. wire goe's to reg. Hot wire when key is on, black/red stripe wire to harness. Higo firsh check volts off alt. rev throttle too check for high lows.14 to 17 volts higher volts means reg is shot. If you have norm volts then you have a short or (mouse Habitat) good luck just keep me updated i ended up rewiring when i changed moters

[JohnnyGunz]

Those cars had very weak alternators. They are at best 60 amp. Not enough to run the car with lights on, heat blasting and radio going, along with the computer and ignition. If you hold the rpm at 2000 will the lights stay bright? If so the alternator is shit. If they continue to dim and brighten its prob the regulator or the wires themselves

[GT800]

i had that issue after i did the aftermarket stereo the stock alternator doesnt make enough from the factory to power the whole car ahh thats priceless make sure if you have to replace it get yourself an alternator for a 3.8 v6 mustang 94-98 i believe they are 130 amp alternators and all you have to do it cut the factory plug off put on a few connectors and vwalah 130 amp upgrade kit

[Higu]

Yeah it seems to be a power issue. If I leave the fan off, IE just the floor heater on, I have no issues. So ikt can't handle the fan with everything else on as well

[GT800]

yup sounds about right

[Higu]

At least it's not a huge issue. Just use the floor heater then. Can do

[GT800]

go to a junkyard and grab an alt from like a 97 v6 stang and throw it in i promise youll feel the difference

[Higu]

eh eventually. I'm broke as fuck. Plus it's too cold out