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mumbles 05-14-2009 08:16 PM

Battery sparked on this noob
Ok, here's the deal. I upgraded my alt to a 120 amp from eagle on ebay, redid all of my wiring between the alt, junction, starter, battery, and ground, added a chassis to engine ground on the alternator pivot bolt, and added a cable from the alt to the positive battery terminal, all with 2 and 4 ga wires.

Just went to connect the terminals and when I did the ground it gave a good spark, and I heard something pop somewhere else. Looks like it started to melt the points where they touched and the sound may have come from the voltage regulator.

This seems pretty bad, so can anyone help me from blowing myself up?



Simpler=Better 05-14-2009 08:39 PM

Sounds like a major short.
Is the positive wire on the alternator isolated from the housing/ground?

mumbles 05-14-2009 08:58 PM

As far as I can tell, yes, they're isolated from each other, but the location of the added ground was the only deviation from a previous poster's setup. They said they used the alt mounting bolt closest to the engine, but that's one of the bolts that goes into the adjustment bracket and for some reason that seemed wrong to me. I can try switching it to that spot though tomorrow morning if you think that might be the cause. I used the pivot bolt on the bottom because it had the most solid metal contact point of the mounting bracket.

Logically speaking, that's the weakest link in the work, so I will probably try that first and of course double check all of my wiring.

I was thinking maybe I left something on because the car has been sitting for a couple of months but nope. I did just notice the car was in neutral, does this make any difference?


mumbles 05-15-2009 01:37 PM

nate dogg and warren g had to regulate
Simpler=Better, now that I know what I'm looking for, I found the short. You were right. The alt to positive cable was touching a screw on the voltage regulator. I could see some of the tape had melted, and the voltage regulator is toast.

So I've got 2 spare voltage regulators from another mercedes site, and was wondering how much of a drop in replacement these are. The model number is "Monark #082 966 028 suitable for 1 197 311 028". The regulator I pulled out says "Bosch 1 197 311 005 el 14v 4c made in germany." I'm gonna drop this in and give it another shot.

Thanks for your help.


Simpler=Better 05-15-2009 05:08 PM

If it fits, it should work. The alternator generates different voltages at each engine rpm; and the regulator calms it down. aka the guts are all pretty much the same.

mumbles 05-16-2009 01:52 AM

I dropped in the replacement, it's 14.5v instead of 14v I believe, verything connected fine and I'm not looking back. She fired right up today though, which was amazing. I haven't heard that sound in several months at least. A/C even seems to work now! Thanks for the help.


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