Really the alternator?

Yesterday after starting my '84 300D the alternator light continued to glow a little. I figured that since it had been raining a lot and the entire car was really damp that things needed to dry out a little, so
after checking to make sure the belts weren't slipping I headed out for my daily 75 mile trip home.
As the trip progressed the light became brighter and brighter, so I became more and more convinced that the alternator was failing, and by the time I got to my mechanic the pad alert light, brake light and the low fuel alert light were all glowing.
Naturally, I can't get ahold of an alternator for the car here (heck, you can't even get a decent bagel in Peoria, IL...) but the mechanic suggested that I could replace the regulator and that might do the trick, but of course he gave me a regulator that's not even close to being the right size...we didn't run a test (too close to closing time!) but apparently the alternator's still putting out since the car ran for about two hours, part of the time with the lights on, and there's still plenty of kick to the starter.
I checked as many grounds as I could find near the dash, and traced the alternator line into the main duct and didn't notice any problems - cleaned the contacts to the alternator and the problem persists. Can the regulator be replaced (assuming I got the right one?) This particular alternator is the 65amp with two pulleys (so of course it costs a small fortune), and what looks like a regulator is a small black box mounted on the back.
thanks in advance,
terry solomonson
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On Sat, 21 Feb 2004 15:01:39 +0000, terry solomonson wrote:

Dunno Terry, but I'm pretty sure that an alternator failure won't cause the other problems you describe - (brake warning light, etc.) You may be barking up the proverbial wrong tree here. Are these the same lights that come on when you first switch on your ignition? Something in that area seems more likely to me. I know, for example on my 300D that if the vacuum is not up to snuff (I know it's not a vacuum problem, bear with me) and I switch off the ignition that the car will happily keep running, and display an alternator light warning.
Have you actually checked the charge voltage at the battery terminals? That's pretty much the last word (or at least the first word) in whether your alternator is behaving itself - if the voltage at the terminals doesn't go over or 14.? (help me out here guys) and still gets comfortably above 12.5 or so, the alternator and regulator are doing their job.
As far as the car running for a couple of hours, with the lights on part of the time, 1) Your engine doesn't much care about the state of the electrics once it's running - you could pretty much shoot holes in your alternator and battery and not bother the engine much (as long as the alternator belt is intact - on mine that also drives the water circulation)- ideal machine for UFO encounters, and 2) if you've got enough battery to crank that big D in the chilly Peoria latitudes, then "part" of a couple of hours with the headlights on won't bother the battery much.
Anyway, just something to think about before you find some mechanic in Peoria who will bolt on a Caterpillar (OK, Caterpillar USED to be big up there) alternator to your D only to find that's not the problem.
Cheers,
Conrad
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Diesels dont need electricity to run, just to start. The problem is your alternator and yes, it can cause those exact dash lights to come on, signalling trouble in the charging system. Most common problem, carbon brushes in the "voltage regulator brush carrier module" are worn down to less than 1/8 inch and no longer making contact. 2 screws, 15 minute job, part should be available at most local part stores 25.oo.....35.oo dolars
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Given that your car started, and that the lights gradually came on/got brighter, you may well have a bad diode (or diode plate) in your alternator. That is a replaceable item at any good alternator rebuild shop, for about $6 plus (a little) labor. When one (there are usually three) of the diodes goes out, the voltage drops by about 1/3, so the battery won't stay fully charged against the drain of your 12+ volt accessories. It is probably worth a look, before investing in a new MB alternator.
Good luck
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Just a note of thanks to the group for your ideas - I finally got around to testing the alternator and it was putting out about 18.5 volts at idle. Couldn't get a new regulator and would have waited until the weekday to get some diodes put in, but I found a rebuilt (on a Sunday in Peoria!) for 90 bucks. Bosch? Don't make me laugh, but hey - 20 year old car, 250K on it? A maniac like me driving it? How long's it going to have to last anyway??
Again, thanks to all.
terry solomonson wrote:

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