Need some advice
My 1993 240 wagon
Alternator not charging more than 13 volts (no lights etc on)
Replaced with a 'rebuild' from NAPA. Still the same
since both alternators are doing the same, could it be an external fault, bad wiring etc.
Hopefully someone can help.
Stranded near Bishop California
Mort

Is there a ground from the alternator case to the engine?
Dan

See this link re voltage drop, should be enough to diagnosis the problem:
http://aimpartsonline.com/reduce%20warranties

Invisibly deteriorated cables, particularly the ground, can cause problems you describe, although reman alternators can be bad straight out the box, it's probably not it.

Mort,
I had trouble with the alternator grounding strap on my '84 245 a few years back and didn't find out the solution until I had a learning experience. One thing you can do is to get a length of 16 gauge stranded primary wire, strip about an inch or so off one end and loop that end around the head of the alternator mounting bolt. Find you a good chassis ground, (one of the bolts on the strut towers), and attach the other end of the wire to that bolt. Make sure this wire is away from the exhaust manifold and any moving belts,etc. If you get a steady 13.5 to 14 volts even when the headlights are cut on, you've found your problem, a bad grounding strap.

I've had similar problems, make sure your ground connections are clean.

Forgot to add
The minimal charge is at idle (13 Volts)with meter a cross battery
when I rev up there is no charge.... drops down to 11.4 volts with meter across battery.

This charge that goes away with higher RPM is really unusual. This suggests:

1) The battery terminals are dirty and you are touching the clamps. It would take a heck of an electrical load to pull a battery down by 1.2 volts from its standard (12.6 volts).

2) The two things I can think of that would pull down the voltage at higher RPM are:

a) If the engine grounds (there should be two) are no good at all and increased ignition draw is using all the available ground connection, or

b) If the new alternator has bad diodes and you are generating AC. Put your meter on the AC setting and see what it says.

You might want to check the voltage at the positive alternator terminal itself if you can get a probe down there while it's running. The other probe should be connected to the chassis (not the grounding terminal). If there is high (charging) voltage, it would likely be an issue with the circuitry between the alternator and the battery. If it's low voltage as you're seeing now, the regulator on the rebuilt alternator is probably to blame. If there's sporadic voltage or no voltage at all, the alternator grounding cable is probably faulty, poorly connected or disconnected altogether.

Those are my thoughts. :-)
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Zach in Vista, CA

1992 245 DL, B230F, LH2.4, M47
1970 145 S, B20B, SU HS6 x2, M41

When you first turn your key on, is your "charging light" illuminated? (not running)
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Post Back. That's whats makes this forum work.

Thks for your reply
The light goes out

Mort. It is necessary for the "idiot" light to be functional for the alternator work on this car. With the engine not running and the key in the run position all idiot lights should be lighted.