1980 300SD. New alternator, battery and charge to battery is little if any. Volts read 11.73 while idling, at 2000 or so RPM will read 12.5 or so. These reading are all WAY low. What could be pulling volts from alternator?

Removed all fuses in fuse panel. Same readings on multimeter.

Anyone with any ideas would be appreciated. I've tried about everything I can think of.

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Rev. Dr. G. Church of the SubGenius
It doesn't take a genius

engine off, ignition on, start tracing your current draws. Isolate your glow circuit as that takes a lot initially, then check/disconnect it seperately to see if the relay is staying on when it shouldn't. Also check dirty terminals - the goo/soup that packs into terminal blocks like the one near the alternator are suspect. Lastly, carefully check the alternator harness - corrosion/frayed wires can really screw things up. I had to replace/fix mine at least once.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Check the condition of the wire/wires that come off the positive terminal on the alternator. They can become brittle and break causing high resistance. I have seen this on my car.

Just for grins clean those brand new battery terminals, both on the battery and on the cables....too much crap will stop a charge to/from the battery.

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Mark
1983 300TD Wagon
Even a broken watch is right twice a day

allright (maybe).

I put a different (good) relay block on and the voltage at idle went to 12.9 at the battery--far better than 11.7 but I think still not where it should be (13.9 at least). On an identical car with this relay block the volts were 14.2.

Battery terminals are clean and shiney.

Is it wiring or am I missing something else?

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Rev. Dr. G. Church of the SubGenius
It doesn't take a genius

What Pete Burton and Omegaman say:

"Lastly, carefully check the alternator harness - corrosion/frayed wires can really screw things up."

"wire/wires that come off the positive terminal on the alternator. They can become brittle and break causing high resistance."

I had a cracked wire that would intermittently lose contact. Local shop finally found it. Not a cheap exercise.

I would make sure to check your ground from chassis to engine in addition to what all the others have stated.

That small connection does one heck of a lot more than one may think.

Actually the ground connection on an alternator is just as important as the positive connection.

Sounds like your getting there. Charge the battery completely and re test. If the battery is run down the voltage reading will be low and appear to not be charging very well but it may be putting out a lot of current trying to charge the battery. Without an ampmeter you wont be able to detect this.