Just noticed that sometimes when I start my '66 F100 that the alt. gauge will temporarily jump to the high side but immediately returns to straight up. Is this normal? Why would it be intermittent? I haven't noticed any charging or lighting issues.
Sometimes if the battery is on it's last legs the gauge will jump to the high side on start-up as it attempts to charge the weakened battery, then settle back pretty quickly.
Hook up a volt meter to your battery and see if it reads the same as your (jumpy) dash guage. If it does possibly wiring - gauge- or voltage regulator problem. If the external meter reads normal and your dash gauge erratic , I would suspect the dash gauge.
If it is a volt gauge there may not be anything wrong, describing it as returning straight up, make me think it might be an amp gauge, if so it is pretty normal for the needle to show discharge upon start, and then return to the middle or a little past. To get to the point, if amp gauge is there any chance it is wired up backward?
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