Battery gauge needle moving up and down


Founding Member
May 20, 2002
Driving my STANG
Was gone from my stang for a month and when I got back it started right up, but the problem I am having is while it is idling, the battery gauge goes up and down for about 5 seconds every 2 minutes. Also when I am stopped at a light with my foot on brake the gauge drops down until I give it some gas.
Any info on my problem would be great.
Thanks alot.'
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sounds like a charging issue.

bad battery, alt, ect should be checked. should get you a good start. can probably take it to autozone or somewhere similar and they will test them for free.
It's the underdrive pulleys. My car does the same exact thing. Just exactly like you described it. Has ever since I put the pulleys on. In fact I plan to take them off because of it. What little power gain they offer is not worth it to me. As long as your battery is strong and your alternator works correctly (at slightly higher rpm's) you will be fine. :D
didnt notice the underdrives, yeah those will do it too.

i just bought a 200 amp alt because the "110" that came with my car wouldnt even hold 9 volts with just my headlights turned on. so weak if the heater came on also it was like holding candles at night.

if you want to keep them i would get a 160 or higher to be safe.