low voltage problem. help!!


New Member
Feb 23, 2010
I have an 89 mustang lx 5.0 and I am having low voltage problems. I have replaced the stock alternator 3 times and tried 3 different batteries and the voltage at idle rarely passes 11.8 give or take a tenth. This causes the car battery to lose all voltage and the car shuts off and needs to be jump started. once its jumped, it will run alright until i shut it off again or it dies, and then it will need another jump start. Any input?? I just ordered a 140 amp alternator to see if that helps and i will be buying a new bigger battery as well.

I can give more details about the accessories I am running if need be.

If i upgrade the alternator and battery and the low voltage still remains, what else might the problem be?
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I actually just bought a 140 amp 1 wire from summitracing, from my understanding the only difference between this and a 3g is that for this one to be activated the RPMs need to reach 1200. Is this the case? or should i revoke my order and get a 3g?
Did you have the system tested? Were the alts bench tested? That will be the only way to know what's going on.
ps. i have a working aod on my car right now id get rid of. i have another one i am repairing that has a shift kit and stall conv so i wont need this one anymore. its stock