Hi everyone,

'91 244 with 5 speed manual transmission here. My alternator died a week ago and I had it replaced by a local garage recommended by a family member (we were out of town at the time so I couldn't do it myself). For the past several months (before we replaced the alternator), my dash lights had been coming on at startup and staying on until I revved the engine. That problem disappeared right after the alternator was replaced, or at least for the first few times I drove the car. I just went out to move the car for street cleaning, and the lights came on and stayed on, even after revving. The dimmed out a little bit after I revved the engine for a couple of seconds, but never went completely out. Any ideas what this could be? Maybe something the mechanic didn't put back together quite right? He said something about checking all the fuses and relays--maybe one didn't get put back correctly?

Thanks
Ryan

Belt tension?
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Post Back. That's whats makes this forum work.

Belt tension seems fine, and a new alternator belt was installed with the new part. Could the battery have been fatally weakened by the slowly dying old alternator?

Verify the connectors on the alternator are tight and the ground is not rusty. Then check the battery termminals. Most autoparts stores will gladly check the alternator output and battery charge.

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My name is Klaus and I am a V ♂ lv ♂ holic

All the connections look good--but where is the ground wire? The Bentley book has a terribly sparse chapter on the alternator. I've got good connections in a big red wire that connects to the passenger-side of the alternator, as well as a smaller black wire slightly above that. Then there's the little black box with a wire that connects back into the alternator.

I just re-revved the engine and the lights that stay on (but dimmer than at startup) are the battery light, the parking break light, the break failure light, and the bulb-out warning light.

"""All the connections look good--but where is the ground wire?"""

There should be a wire coming off the bottom inside(near the engine).

Here is a pix showing it looking up from the front of the car from underneath.....the Blue wire with the red end at the alt attachment.

http://cleanflametrap.com/oilpan/images/oilpan26.jpg

another view of just the wire

http://cleanflametrap.com/alt2864.jpg

back of alt.

http://cleanflametrap.com/alt956.jpg


Thank Art for the Great Pix

Thanks. I removed the small red and ground wires from the back of the alternator and they both look very clean. gave them a wipe and reinstalled. Problem persists. I couldn't get to the ground wire where it attaches to the engine block. I doubt this was removed when the new alt was installed, so could this really be the source of the problem?

It's significant, I think, that the only lights staying on are the battery, e brake, brake failure, and bulb indicator.

"It's significant, I think, that the only lights staying on are the battery, e brake, brake failure, and bulb indicator."

That's a good observation, because the current drawn by those 4 lights is what allows the alternator to begin producing voltage as the engine is started. That "start-up" current comes into the alternator D+ terminal on a small Red wire, to do 2 things:

1- D+ first leads to a ground path for the Batt light (and the other 3) TO and thru the alternator to ground. Those 4 warning bulbs have battery +12V "hard-wired" on one side, so the bulb current flowing thru alternator D+ to ground is what allows it to start producing voltage as it "spins up".

2- Then, once the alternator is putting out voltage, the D+ terminal (that was a ground) rises to alternator B+ (output) level and reflects the +12±V back to those 4 bulbs. Since there is now voltage on both sides of the bulbs, there is no current flow and they go out.

If those 4 lights don't go out when the engine starts, the alternator is not putting out. [The fact that they lit up normally with the Key On says that the alternator ground path (including regulator brushes) is OK.]


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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Could the problem be in the small red wire that runs from the idiot lights to the alternator?

I would ask for your old alternator back.

Odds are that the only thing that was wrong with it was that the brushes were worn (too short) and as such was no longer charging.

Just replace the brushes or get a new regulator/ which comes with new brushes.

"Could the problem be in the small red wire that runs from the idiot lights to the alternator?"

Not unless it's broken and shorted to ground someplace before it gets to the alternator. The fact that the warning lights come on like they are supposed to suggests the wiring is OK. The lack of voltage output suggests (to me) that the "new" alternator is a dud, which is not uncommon with chain store rebuilts.

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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Hi Bruce,

Thanks, this is really helpful.

So what you're saying is that if those 4 lights light up with all the other dash lights with the key at ON before I start the car, then the ground path for the alternator MUST be OK. SO that eliminates a grounding problem with the alternator itself, correct?

In that case, does that narrow the problem to the alternator itself? Or is there another issue that could be hiding (maybe wiring?)

I just tested the battery and the alternator with a multimeter. The car was driven about 20 highway miles before I parked it last week and hasn't been driven since (until yesterday, when I discovered the problem), so the battery should have been close to fully charged. The battery reads 12.1 with the car off and 11.7 with the car running at idle. The reading remains the same after revving the engine above 3k RPMs. The reading at the big red alternator wire is 11.4.

So what does this tell us? The alternator is dead? Since it's not running and reaching 12 volts, it's not shutting the lights off? The alternator belt was replaced with the alternator and seems pretty taut to me. Are there other multimeter readings I could take to hone in on the problem? Or does this seem like a pretty cut and dry dud alternator?

Those are not satisfactory voltages. A healthy battery should show 12.4-12.7V at rest, dip to around 10-11V as the starter operates, then rise to 13.5-14V as soon as the engine starts. Your alternator is not charging. If all wiring connections are OK, it's pretty sure you have a bad alternator.
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Bob: son's XC70, dtr's '94-940, my 81GL, 83-DL, 89-745(V8) and 98-S90. Also 77-MGB and some old motorcycles.

Try reading the battery voltage with the engine running at idle and then up the RPM's to about 1500. You should be reading 14+ volts if the alternator is working.
Dan

When your key is on, engine not running is the alt charging light illuminated? That light must be good for your alternator to produce a charge. If it is, then I would take the car back and they can test if its charging. I wouldn't tell them you did anything but noticed no charge.
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Post Back. That's whats makes this forum work.

Yes, the battery light is illuminated when they key is on, engine not running.

Some times wires look good but they are not. I would run another ground wire just to check it out. Also check you ground wire on the battery. It sounds like a grounding issue.

Just pulled the ground wire to inspect. Looks sound except for a bald connection at the alternator end. I cleaned the engine-end contacts and reinstalled. Problem is still there. Does the end of this wire look bad enough to cause ground problems?

Also, the dash voltmeter is reading 12-ish, and it usually reads 14-15.

Thanks. Can you say a little bit more about how I should do that?