Join Date: Jul 2001
Location: Southern California
Charging system can't handle load? - new 3g alt and battery
I am sorting out my 1990 Mustang convertible and am having an electrical issue. With the car running with lights and a/c on the volts at the battery drop to 12.3 Volts or so. With lights and a/c off, it reads almost 14.4 volts. This is at a stock idle - car is warmed up. I listed the volt reading below for reference.
This is on a brand new batt and 3G alternator - old battery was toast from sitting and old alt had a bad diode but did the same readings aproximately but with a smaller alt pulley. The 3G conversion was done by the previous owner. This is a vortech car so the alt is under the smog pump. I took the new alt back to the parts store and they load tested it to confirm it was good. The old one failed this test.
The power and ground cables on the batt are HUGE - definately upgraded...looks like a 0 or 2 gauge? Fog lights are not hooked up, there is a stereo system in the car - two amps, a crossover and head unit hooked up to power. Turning them on or off doesn't affect voltage readings.
engine running at stock idle:
no accy: 14.4V
just a/c or lights: 12.8V
a/c and lights: 12.3V
no accy, key off: 12.93V
no accy, key on: 12.38V
Fan or lights on, key on: 12.19V
Fan and lights on, key on: 12.05V
With a new batt and a new 3G alt I know I have an issue somewhere - i have another 90 stang with OEM alt and it's at 14.4V until I have lights, a/c and something else on. Where should I look/test? I'm confused as the issue seemed to point to a bad alt bu obviously it's somewhere else?
Thanks the the help!