bad alternator?

[monkr63]

I think I have a bad alternator on my 1988 190e 2.3, but tell me what you think.

The problem: The car won't start. It won't even turn over. When I jump it, the car starts up with absolutely no hesitation but dies immediately when the jumper cables are disconnected. It runs fine as long as the cables are connected. Sounds like a dead battery, right? Wrong.

Here's where it gets interesting:

With the ignition key in the 'off' position, the battery shows 14 V. All of the instruments work, including the power-hungry headlights, CD player and windshield wiper.

With the key in the 'run' position, (but with the car not running), the battery shows 14 V. Same situation on the instruments.

With the key in the 'start' position (starter not engaged), the battery shows 11-12 volts. The cable connector (between the alternator and the battery) shows 2 volts. None of the main instruments work; the warning lights are at half power and the 'Check Engine' light is on. If I engage the starter, it does nothing but when released, I hear the clicking sound. (Note that I got 14 V when I checked at the cable connector with the car in 'off' and 'run.')

With the key still in the 'start' position, I tested from the neg. terminal on the battery to the pos. connector on the cable connector: 11-12 V. When I tested from the pos. terminal on the battery to the neg. connector, I got 2 V.

To me, this indicates that the alternator is grounding out. Is this correct? Is the alternator shot or just the diodes? Or is it faulty wiring between the ignition (start postion) and the alternator?

What do you think?

Please help. I need this car running, not sitting in the driveway!

Thanks.

[deiseldwarf]

At this point, I would be looking at the state of my wiring harnesses. If the wiring that goes to the alternator is at all in disrepair, I would look inside of the harness and see if there are bad wires in it.
In my opinion, you have a good instinct, in beleiving that the thing is grounding out. Also, I was curious as to whether you tested the out put at the alternator itself. If it's a regular bosch, it ought to have about fourteen volts, or there abouts.

[monkr63]

The wiring is/was all ok. I decided to trust my gut and I put a new (rebuit) alternator in yesterday. Everything works right now.

Better yet, my mechanic wanted over $500 to do the job ($325 for parts, $175 for labor). I bought the alternator at www.autopartswarehouse.com for $150 and did the installation myself in about 1 1/2 hours. Not bad, huh?

Thanks.

[ricebike]

yeap, not bad @ all... y went to an online supplier? your closest autozone don't have it in stock? + they carry a lifetime warranty too...

I was gonna suggest removing the alt & have it bench tested @ your local autoparts store for free... but you already ruled it out!!!

some vehicles are a biatch to get to the alternator(some imports)

[deiseldwarf]

Congratulatoins on your repair. I hope that it holds for you. Those alternators, depending on the year and model can be tough to deal with. best of luck.