1976 450slc
Normal voltage output when no accessories are on. Low voltage when any accessory is on.
Alternator is good. Ground good. Belt is tight.
This forum has been helpful in the past, so I'm hoping to get advise on my problem.
I have low voltage whenever I have an accessory turned on – headlights or auxiliary fan or blower fan.
Here is what happened:
This summer, I had a dead battery. After a couple weeks of driving around town, dead battery again. I could tell starting motor going slower towards the end. Test at autoparts store says battery fine, alternator only putting out 12.5 volts.
So, I had it rebuilt at the local electric rebuilder. Car seemed to work great. 3 weeks later, dead battery again.
Took to my indy mechanic and he checks things and says bad alternator. I take alternator to rebuilder and bench tests fine under load. 13.8 amps. He says it’s the car.
So back to indy who puts it back on and still low amps when an accessory is on (ok when no accessories). I take car to rebuilder who does some tests and thinks it’s the aux fan.
Back to indy and unhook fan, same issue with headlights on. So we decide to try another alternator from autoparts store. Same results as original alternator.
So to summarize:
13.8 volts at idle with no accessories. Checked at alternator and at battery.
Turn headlights on, 12.8 volts. Aux fan, 12.6 volts.
Belt is tight. Indy says idle is fine and all systems check out, including ground. Everything is stock. No energy leak when car is off. He’s stumped.
I have a voltmeter on my charger. I confirm the volt readings at idle with no accessories, and with either accessory on.
Any ideas where to start to diagnose? My first step is to buy a good voltmeter.
Normal voltage output when no accessories are on. Low voltage when any accessory is on.
Alternator is good. Ground good. Belt is tight.
This forum has been helpful in the past, so I'm hoping to get advise on my problem.
I have low voltage whenever I have an accessory turned on – headlights or auxiliary fan or blower fan.
Here is what happened:
This summer, I had a dead battery. After a couple weeks of driving around town, dead battery again. I could tell starting motor going slower towards the end. Test at autoparts store says battery fine, alternator only putting out 12.5 volts.
So, I had it rebuilt at the local electric rebuilder. Car seemed to work great. 3 weeks later, dead battery again.
Took to my indy mechanic and he checks things and says bad alternator. I take alternator to rebuilder and bench tests fine under load. 13.8 amps. He says it’s the car.
So back to indy who puts it back on and still low amps when an accessory is on (ok when no accessories). I take car to rebuilder who does some tests and thinks it’s the aux fan.
Back to indy and unhook fan, same issue with headlights on. So we decide to try another alternator from autoparts store. Same results as original alternator.
So to summarize:
13.8 volts at idle with no accessories. Checked at alternator and at battery.
Turn headlights on, 12.8 volts. Aux fan, 12.6 volts.
Belt is tight. Indy says idle is fine and all systems check out, including ground. Everything is stock. No energy leak when car is off. He’s stumped.
I have a voltmeter on my charger. I confirm the volt readings at idle with no accessories, and with either accessory on.
Any ideas where to start to diagnose? My first step is to buy a good voltmeter.