I bought a new alternator (rebuilt) at the parts store this weekend and replaced my old, fried one. (It got fried because an idiot crossed the terminals on the battery when jump starting another car).

Anyway, The alternator I bought was listed as compatible for my car but it was rated at 55 instead of 65 which is what I have been reading on this forum is correct for the car. The back of the new alternator doesn't look the same as the old one but the cable plugs in just fine. I put the thing in and the car starts, battery charges but the following problems were observed.

1. The ABS Light comes on and stays on
2. The AC fan works but there is no cold air
3. The tachometer doesn't work at all but the rest of the instruments work.

My questions are: Did I buy the wrong alternator? Could it be the voltage regulator? Could the reversing of the polarity have caused something more than frying the alternator? Would it be best just to go ahead and replace this weak alternator with the correct one?

Thanks for you help in this matter.

dave,

I don't see how a lower current alternator would cause the other problems. It puts out the same voltage as the higher current alternator. The lower rated alternator just won't put out as much current at high loads. I wouldn't call it a weak alternator. It just doesn't have as high output current at full load.

The parts that don't work should work without any alternator in the car. They would work off the battery voltage if they weren't damaged. It could be that reversing the polarity damaged them. So I would look at them before replacing the alternator.

P E H

Thanks for your help. I think I will take the car to my trusty mechanic and get him to fix it. This is sort of beyond my abilities. Tracing electrical problems is best left to someone who knows more than I.

I was just hoping it would be something simple.

No more jump starts.

I think at a minimum I would check the condition of the fuses in the fuse box. That may have some impact on individual components acting up. Easy and cheap enough to do.....

Ken300D

__________________
--------------------------
1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

I did check the fuses and didn't find any that were out. But I have replaced some before anyway and had good results. I could just go ahead and replace all the fuses and see what happens.

Are there some in line fuses on the ABS, AC or tachometer?

I don't know about the other components, but usually the A/C compressor clutch is on a fuse.

Ken300D

__________________
--------------------------
1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

I'll certainly check that for sure. But replacing all the fuses might just be a good idea. I did replace the tach fuse and the thing still doesn't work and the other stuff on that fuse does so I think I fried the tach maybe. I don't know how tachs work so I don't know for sure.

Check the red fuse on top of the OVP relay.

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Thanks for the advice. What is the OVP Relay?

I figured out what an OVP is and replaced the fuse. It worked. But now, I turn on the radio and the auto antenna doesn't go up. I looked at the fuse box and the fuse for it is working. Is there an inline fuse somewhere or did I screw up the motor?