I am having a hard time finding my problem... I put a new alternator in my 81 300sd and had battery tested as good (its only 9 months old)

... my battery light keeps coming on at idle and im only seeing 9 volts coming from my alternator with AC and lights and radio fully on at idle @700rpms

WIth my ac off the battery light and brake light and light in the middle of those two(circle with lines around it) stays on...

multimeter from positive on alternater to ground says 9volts

mulitimeter from battery terminals while running say 15.4 volts

battery when turned off says 14.2 volts

blue wire seems to be on tight but i was thinking this could be whats wrong... is there a procedure for testing this wire..

i tried to unplug glow plug relay and noticed that my electric fan speeds up and when plugged back in slows down.. i also seem to think my fan is not shutting off at all... just stays on all the time but the temperature is 90 today...

Any thing im missing or suggestions... the belts are tights and i checked everything i could..

16.5 volts is to high, it will cook the battery.

Pull the alternator and have it and the battery tested.

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my old alternator said the same thing as well.. this alternator is brand new and i put it on today... is it a dud.... cause its the exact problem my old stock unit had...

DVM could be off. Try another one.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I have purchased new and reman parts that were bad.

You did have it bench tested prior to install, RIGHT?

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

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alterntor they said tested fine at 14.9 volts... seems high to me... also my battery voltage is still high after i left the brights on for 20 minutes... i still had over 14 volts... Could this be a overcharge protection relay or does this sound like dead battery cells.... The wires going from alternator are brand new 10 gauge wires and all make great contact on clean surfaces.

the blue wire grounded to the negative battery cable is reading 2 volts while running and 0 when key is off.

anything above 14.4 volts is out of spec and points clearly to a defective/failed voltage regulator.

you can replace just the vr, no need to swap the entire alternator. vr's are usually inexpensive. visit your local alternator and starter rebuild shop, i bet they even have the correct one in stock.

With engine running, check both DC and AC Voltage across the battery terminals.

If the DC is a little high, it is likely to be a regulator.
If the AC is above 100mVAC, then a rectifier diode in the alternator is failing.

Check your grounding as well. (Especially the chassis-engine ground strap.)

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

16.5 V will cook a lot more than the battery. You will be soon changing almost every incandescent bulb in the car. You are also on the upper limit of most automotive electronics.

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2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
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just had it tested again at a different auto shop and the guy said that there were no volts coming from the alternator... this still doesn't explain why my battery is fully overcharged... new alternator has been ordered and will try it tonight...

got new alternator in and now my starter just clicks and doesnt turn over... I am starting to hate this car lol... i jumped the wires on the terminal block with a remote switch and still nothing... My battery has 14 volts...

Sounds like a bad ground all along since it is unlikely for 2 alternators (1 new) to behave the same way. Check and tighten the ground strap on the driver's side transmission bell housing.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Also check and clean battery terminals including chassis ground.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Test your volt meter against another unit.


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your common sense knowledge would of saved me some trips to auto store... my multimeter was 2.2 volts off... tested on three other sources... just bought a new one and now my electrical system checks out... but i still have no starting even when i hook up my 1200cca jump box to my unhooked battery cables to bypass battery.... same thing when i jump wires 1 and 3 on fender... also my battery light and previous two lights are still coming on..... Im adding a new ground wire to my passenger side and also cleaning up the old one.. Shoulld i run new battery cables to starter to eliminate a short... my old cloth wires seemingly look ok... I upgrades the alternator wires to 10 gauge wires...