Dear guys,

I need some advice about the electrical supply for my 1.2 8V Mk1 Cabrio. She has eaten 3 altenators previously. During the 4th replacement, I added a voltmeter wired to the dash and here are my findings during operation:

1. During normal engine running and standing without any load, it reads 13.6V.

2. When signal repeater switched on, the voltage goes between 12.2V and 13.4V. When I switched on the hazard signals (all signal lights on), the voltage went just to 13.4V although all lighted on whereas compared to by turning on the signal, only one side lights switched on.

3. Switched on the dimmer night light (without the head light), the voltage goes to 12.6V and if the head light is on, it just go 0.1V lower

4. Press the brake pedal, the voltage goes from 13.6V to 12.6V

5. Switched on the air conditioner, the voltage goes from 13.6V to 13.4V

Referring to No.2 and No.3 above, is there a possibility for a wiring problem? It's because the voltage differences are too high. If yes, could you please give advice on what am I supposed to do to identify the problem. I've also check the parasitic drain and it doesn't happened.

Your opinions are greatly appreciated. Thanks.

That sounds okay to me. The voltage never goes above 13.6v and never falls below 12.6v. I don't understand why the hazard lights seem to use less juice than the indicators but that may be how it works.

If the alternator is failing and it's not just because the alternator is cheap/badly reconditioned... it can only be an problem with the regulator/rectifier.

Is you alternator brand new each time, or is it a reconditioned part? Who makes it?

Is the regulator/rectifier brand new (new one comes with the alternator) or are you using the same ("old") one each time... (although, as above, it sounds like it's working okay).

When the alternators "die"... what goes wrong with them? Do they burn out or just stop charging the system? Is the alternator belt pulley original or different?

Measure the voltage across the battery terminals with the engine running at fast idle (~2500/3000 rpm). It should be 14.6v. What's yours say?



Ralf S.

Dear Ralf,

Thank you for your response. As for your questions:

Is you alternator brand new each time, or is it a reconditioned part? Who makes it?
They're all Magnetti Marellis, from chopped shops. All of them working finely in the beginning. After a couple of months, the symptoms surfaced again.

When the alternators "die"... what goes wrong with them? Do they burn out or just stop charging the system? Is the alternator belt pulley original or different?
The rectifier doesn't charge or going at 11+Volts only. The altenator felt extra hot. Belts used are standard.

Measure the voltage across the battery terminals with the engine running at fast idle (~2500/3000 rpm). It should be 14.6v. What's yours say?
This one I haven't done yet. I'll do and update the result ....

Thank you for your advice.

Check the big wire from alternator to battery , and the big negative wire from battery to engine.
If either of these wires are cracked under the insulation and make intermittent connection that will cause alternator failure.
That is most likely what is happening with your car as you have had so many alternators fail.

jackwhoo said:

Check the big wire from alternator to battery , and the big negative wire from battery to engine.
If either of these wires are cracked under the insulation and make intermittent connection that will cause alternator failure.
That is most likely what is happening with your car as you have had so many alternators fail.

Click to expand...

The earth from the battery might not be very good. I'd remove the negative cable where it's attached to the body and clean it and the point it touches the car, to make sure the connection is as good as it can be. Once you re-attached it, put some petroleum jelly (Vaseline) or other type of grease on it, to stop it corroding in the damp air.

If the earth isn't clean you will have more resistance which could be the cause of the overheating alternator.

Ralf S.

Jack and Ralf,
Thank you for the advises. Will do that wires checks the weekend.
Appreciate that very much!