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1983 240d
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Discussion Starter #21
A little update, and a few further questions. Replaced my battery under warranty (with considerable headaches involved). Checked voltage at the alt plug, all 3 have approx. 12v (D+ only with key on). Good continuity from engine to chassis. Checked voltage at cabin light (which has at times been squirrelly), good voltage there too.

Where else should I be looking for unfused current?

Where does the purple wire (from starter) go? I am guessing ignition switch? If starter activates, does that mean purple wire is sound?

If I have a short to ground (worn wire touching chassis or similar) will I still get proper voltage readings?

I will bolt up a good alternator tomorrow, but I am hesitant to run the car and then just fry a different alt.

The glow plug indicator light hasn't worked for some time now, (the relay checks out according to the diesel giant tutorial) how can I test the continuity of that wire? And could this problem be related?

Thank you everyone for the suggestions so far, I would be nowhere without all the information and help contained on this site!
 

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https://mechanics.stackexchange.com/questions/27815/can-a-weak-battery-destroy-an-alternator/27833#27833

This link will give the length and breadth of the trouble.

Basic tests, is there any power drain on the battery in the car when not in use. And is the battery a heavy duty type which when part discharged could overload the alternator on first start up. Next double check all connections B+ clamp to cable- cable to starter- starter to alternator. These would normally fail when cranking and be obvious because no start, but alternator to starter connection defect won’t show up cranking. If alternator plug has a corroded spade coupling it can overheat resulting in open circuit or intermittent fail ,this will then be the source of problem. To check for power drain check voltage after car standing for a day or so. If batter is drained it may demand an overload current , which explains the melted solder on the rectifier pack.
 

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1983 240d
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Discussion Starter #23
I've checked all connections from battery to alternator, and they appear fine. I am currently working with a new battery (Walmart Maxx H8), new (to me) starter, and new (to me) alternator, all of which bench test fine. I am hoping to get ideas for other places--relays, wiring, components--which would put a similar load on the alternator and cause overheating (and thus a dead battery).

I am curious about the glow plug circuit, since I have no working indicator light.

Antenna perhaps? Is searching for continuous/unfused power even the right thing to be looking for?
 

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Glow plug circuit is one to consider. The lamp circuit is only wired as a monitor parallel to a bi metallic thermoswitch, current drawn to the glow plugs also provides voltage which heats the bi-metallic contact strip. So this part of the circuit is unlikely to cause issues here.
However the glow plugs themselves will draw 60 amp (4 cylinder) for 10 ,20 or 30 seconds. This means that the battery will immediately demand recharge current of this plus 350amp for the cranking start duration. Normally the internal resistance in the battery and alternator windings limits this charge rate, But some modern batteries are designed for rapid recharge for stop start technologies and countless other high demand modern systems. So the battery may overload the generator if it is not ‘Balanced’to the alternator.
Even if it doesn’t immediately fail the high currents generated will typically shorten the service life of electronic components. Also as a sleuth technique. Go back to the first event, and consider what happened before that. Test the correct operation of all circuits. Beware of using jump leads with a seriously flat battery in the car.
 

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Discussion Starter #25
I think part of the problem I am having is simply applying the wiring diagrams (from the Startek site) to the actual auto body. I am a visual person, and can fairly easily understand what I can see (for general problem solving). Looking at the diagrams, I can see where a wire ultimately goes, but the route on the actual auto body it takes to get there is not always readily apparent.

I guess I am expecting to find a burned-out connection or wire somewhere, have an "ah-ha!" moment, and... problem solved. Instead, I am finding that everything looks and works fine (until it doesn't and I am stranded in the Lowe's parking lot, again).

So clearly my diagnostic methods are suspect and I need to learn some new way of working through the problem, since time and time again, everything tests out fine and then burns out the alternator in short order. Because of that, I've been reluctant to just put the new components on and go, because that hasn't worked out in the past 2 years I've had this problem.

That said, the alternator is back on, and charging at idle, at least for now. All dash lights come on except for the glow plug indicator.

I did notice a few things... I started doing a parasitic draw test, and with no fuses in was (at first) getting a reading of 3mA. At some point (fuses 8 and 10) while putting the fuses in 1 by 1, my DMM went to zero, and I couldn't get an amp reading after that at all. Not sure if there is suddenly something wrong with my meter or if this indicates an electrical problem. I'll try again later, and look for another meter to use.

Also possibility related, I sometimes get a very minor shock from the doors when entering/leaving the car. I've always just chalked that up to dry weather and static, but perhaps it is something more?

Also the seat belt light seems a bit squirrelly, staying on after seat belt is fastened periodically.

Sorry for my long-winded posts, as I try to work through this!
 

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Hi , you are evidently traumatised by the fault history.
Wiring systems have evolved to simplify the process of protection and repairs. Essential driving circuits have design features to eliminate critical defects while driving, like robust cables , connections etc so these should be checked for and modifications , rerouting or additions (permanent live feed to radio is a typical one to check) . Other circuits are given fuse protection so as to isolate any damage from the core. So here power supply up to fuse boards needs checking along with the rating of the fuses.
For the sake of restoring faith in the system, consider installing ammeter so you can observe in real time the charge rate. My money is on the battery having been the problem, perhaps exacerbated by a current drain.
 

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Discussion Starter #27
you are evidently traumatised by the fault history.
Haha! Yeh that is mostly definitely true. Too many times stranded, not enough hills. So far the battery seems to be charging, but I am waiting patiently for the other shoe to drop. A few little squirrelly things make it seem like the fault may have just moved on down the line somewhere.

Getting a slight shock after driving, I’m guessing would generally indicate a bad ground somewhere, however I have gone over all the grounds I know of and don’t see anything amiss. It’s not at all a dry winter here which makes me think the likelihood of it just being static is slight.
 
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