I'm talking to a guy about a 1991 300CE (Which I have not seen - out of town) and he said he reversed the battery cables and blew out the main computer. My question is, When this happens what all can go wrong with the electrical system, sensors and computers. If I buy this car what am I up against?
Thank you,
Danny

I would press him a little more to find out if he means the "engine control module" when he says "main computer".
It seems like a lot will fepend on what was switched on when this occurred and how long the cables were connected. There is the fuse in the overvoltage protection relay which may have blown and protected a few of the major systems (engine control unit, ABS and SRS control units, etc. Depending on what may have been activated there could be problems in the overhead dome lamp (which has a small timer), the central locking and alarm systems, and the radio.
What does he state is wrong with the car, no start or???????

Gilly

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All the info I've gotten so far is by email and little of that. However, he said the cars was running fine and everything worked ok before the mishap, then he says it won't do anything.
Does this sound right?

No, it doesn't sound right. He has to expand on "won't do anything". He's saying the engine won't crank at all and not a single electrical system operates, in otherwords it's like the car now has no battery at all?
In that case either there was a car fire and the harness was destroyed (unlikely) or there is some simple reason for it, something wrong with the battery cable or something. It sounds like an interesting project. The condition of the car is otherwise OK? Just curious, did the owner do this to it, or a shop?
You may not know, that's OK.
Get some more info out of the guy.
I saw this happen once to a 140 chassis S-Class V12 (S600),
big bucks to get it so that (for the most part) everything worked, lots more computers on one of those of course, luckily fuses protected the engine modules. It was towed in, but I had it running in under a 1/2 hour (fuses in the Base Module), but there was lots of random things that didn't work (locks, light, radio, etc etc) most of which was traced to control units. Had almost $4000 stuck into it in diagnostic time and module$$, Only thing I recall that didn't get fixed was the cellphone, needed a new handset and owner (who had just bought the car used in perfect shape when someone at an airport botched a jumpstart, which was needed because he didn't shut the dome lamp off) decided he wasn't really interested in the factory phone handset for $1000.

Hope this all help give a perspective, I think the CE is alot simpler than a V12 S Class, shouldn't run into this kind of money, not unless the harness melted for some reason, but reverse polarity I don't think would cause this much damage to wiring, just some modules. Luckily on something older like this you can consider using used parts, it's not all coded to the car like newer stuff is.

Gilly

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THX GILLY,
I'll get more info over the next two days and get back with you.
Again Thank you,
Danny

Thanks Takmiya.

Been there, done that. Doh!

1) Blew OVP relay fuse (thanks OVP!)
2) Fried Alternator
3) Fried original Becker
4) Melted alternator wiring harness.

The whole so called 'computer' thing may just be the OVP relay fuse.

Don't do that!

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