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Battery Voltage drops severely when warmed up

2051 Views 1 Reply 2 Participants Last post by  Tranquillity
Hello All,

I recently picked up an '88 Shelby-Z with the intent of putting all of the shelby goodies in my '84 Laser XE, however, I need to drive the car for a few weeks since both of my Lasers are out of commission and waiting for parts. After a few days of driving I am noticing some very strange charging system behavior. Car starts and runs fine in the morning with the battery gauge reading a decent level(1/3 of the way up but well inside the operating range). At night time while driving with lights on the voltage drops as the car warms up to the point where the gauge falls below the operating range, the radio cuts out when I hit the brakes or perform a similar additional electrical load, turn signals stop blinking, headlight motors do not retract when lights are turned off. This latest time the car even drained to the point where the lights were vitrually dimmed to zero, the tach started going nuts and the engine finally died (Not enough juice to run the computer) At this point the voltage gauge read at the bottom mark (8 volts). The car behaved as though the battery was completely drained and dead. Next day, I try the car and it springs back to life! Headlight covers close, battery gauge reads 1/3, car runs fine. If the battery was truly drained from the previous run, this would be impossible. My only theory is that the alternator or it's diode/triode circuit actually starts to short out as the car warms up but "un shorts" when it cools back down. The warming up seems related to the amount of load as my morning drive is uneventful, but the drive home with headlights causes problems. Perhaps the alternator only heats up when it is under a charging load and this causes the alternator itself to start loading the battery and stealing power from the rest of the car? :confused: Anyone experience anything like this before? I haven't had time yet to do the obvious, which is testing the alternator. Just wondering if anyone has had this behavior or if the SMEC may be partially to blame since it's involved in the charging circuit as well. Thanks in advance for any help/info :D
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Check your codes. I'd say it sounds like your voltage regulator may be bad. May not be giving enough charge when you start using your lights and such.
And yep, voltage regulator is in the SMEC. You can get an external one you can just install without having to replace the SMEC though. Friends car had this exact problem. Was the Voltage regulator

If you're unfamiliar with codes - http://minimopar.knizefamily.net/fault/
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