240 Battery Drain Issues

[regent]

Is the warn light operational (does it illuminate when ignition is on while engine is NOT running?
If the alt is not putting out enough, this could be a bad rectifier, bad V-regulator, worh brushes or an open in the exciter circuit. Your diagram should be available here on the forums. I will look it up too.

[regent]

With the warn light and alt operational, it may still be possible to have a voltage drop in the negative loop.
These are two basic assessment tests you could perform to look for excessive resistance in the charge circuit:
At around 2,000 RPM and everything turned ON (headlights, heater fan, wipers, radio) and only rear defogger OFF:
1. Measure between G+ and the battery positive post. Any reading below 0.3 volts is OK
2. Measure between battery negative post and the generator body - a good reading is below 0.1 volts.
The above tests will give you an idea of a charging problems caused by an issue outside an alternator (assuming the alt is otherwise operational.)

Sorry I could not locate your exact electrical here but you could refer to the attached for basics. Hope some other member may chime in.

[bfrancese]

Thanks for this. I will test tomorrow. I'm also going to have the alternator tested one last time as it's been about 3 weeks since the last test just to be sure. We replaced voltage regulator about 3 weeks ago.

As for the warning light, the battery warning light always pops on at start up + then goes immediately off (like usual at start up), but the "light bulb" warning light I've read about in a few manuals + forums (not sure if it is applicable to my 1990 240) does not pop on. Not sure if that has anything to do with it.

I'll do the following tests + report back.

[bfrancese]

So after a few tests I decided to just replace the alternator. Both the alternator + the battery were holding at the same voltage + I had the alternator tested again at AutoZone. The diodes passed fine but the regulator did not pass. It was holding steady at 12.3V.

After successfully getting a new alternator on + doing some load tests the battery held steady @ 13.8V as well as the alternator.

I was curious so I pulled the old (but only 3 weeks old) regulator out of the old alternator + one of the brushes had sheared completely off.

There is still a short in there somewhere since the interior lights still do not come on. I've left one of the wires that goes to fuse number 8 off the fuse to disengage the interior lights + central locking (not really needed for driving anyways) so as not to get any drainage off the battery.

We will see how it goes.

[regent]

Glad you found the culprit.
With one brush hanging (or barely touching the ring) your alt's exciter circuit was (next to) open; even then, the alt was still putting 'something' out - due to residual magnetism in armature - just the bare minimum that can turn the warn lamp off to get you confused, and yet insufficient to take load. (I was assuming your gen was new and 100% OK, so I did not want to challenge that.)

Now, 13.8V at the G+ is not bad - just a bit on the low side: it may be possible that the battery is not completely full; as the battery reaches its fully charged state, you should read 14.4V and up at gen with load. If this does not happen soon, I suggest charging the battery to full capacity with an external charger, and re-installing it.
As winter temperatures roll in, this is very important.

Thanks

[SmokinJazz]

My #8 fuse kept shorting and blowing in my 93 240. My problem was the wire behind the glove box leading to the light in the glove box. The duct tape that originally held the wire in place against the top of the glove box had worn out and the wire got caught up in the support mechanism that holds the glove box door when it is open. The wire eventually wore through and grounded against the frame. Re-taped the wire and taped it against another wire bundle to keep it out of the way - now I have no issue with the #8 fuse. Also - when the fuse had blown and the glove box was open, it would "bing" as though one of the car doors were open and the key was still in the ignition - that was odd behaviour, but certainly made it easy to identify the glove box as an initial investigation spot.