[fast5liter]

Got a 91' 5.0 that runs great. Whenever the engine is running above 1ooo rpm's the volt gauge stays around 15. But everytime it idle's whether it's parked or at a stoplight it drops into the red and the lights dim, radio cut's out ect.If I have the battery charged at autozone it will fire up for a couple of days then has to be jumpstarted everytime after that. I had the same problem with my 89' 5.0 . I do have underdrive pully's. Would that make that big of a difference putting just the stock alt. pulley back on?

[93hatch]

most people do the underdrive pulleys and dont do the alternator pulley, i didnt do the alternator pulley and my lights still dim, but it never drains my battery enough for the car not to start, time for a 3g upgrade

[nolife]

Based on your statements, I would say that yes, your alternator is not putting out enough power to maintain the battery charged. Swapping the alt pulley back to the standard one would probably solve your problem. If not, and your battery and terminals check out fine, you may need a 3G upgrade.

[86gtconvert]

you can get a small set up to go on a stock alt in a fox to make it a one wire set up for about 40.00 which is cheaper then buyin a new 1 wire alt.. place here called start rite electric builders has them i used to have them

[Speedstang302]

i had the same problem, wasnt using the alt underdrive pully, turns out the wires from the battery to the alternator were chard and the alternator shit the bed...new alt and wires solved it..

[hh668814]

My 89' does the same thing and i have underdrive pulleys, unless i step on the pedal a few good times before i turn it off it doesnt like to fire back up.

[trueblue01]

Have Auto Zone test your alternator and battery.