concor

Hi guys, my car (928S '84 EU) is acting up. Three things are odd:

1. The alternator light stays on, even when the car is turned off
2. When I turn the key halfway, all the ligths on the dashboard turn on for only a split second. Normally they stay on. The car does start though if I turn the key completely.
3. Over 3.5 amps of current leakage whith everything off. Interior lights off, only the red door lights and the alternator light is on.

​​​​​​The alternator light turned off after I charged the battery for a day. Now, at 12.7 volts it's on again.

I removed all the fuses and relays one by one and it stays at 3.5A. Although it was about 0.2A less I think with the window regulator relais removed. Which turned off the door lights.

I made a video to illustrate the problem and thanks in advance!!

gazfish

Possibly a bad voltage regulator on you alternator, does the current drop significantly if you disconnect the 14 pin connector in the engine bay?

ZEUS+

Possible ignition switch. Try disconnecting switch and recheck.

Alan

Certainly seems most likely to be a failed alternator regulator - you could remove the blue wire from the 14 pin connector (or off the alternator) and see if the leakage goes away. For a better check: with it disconnected from the alternator if you ground the blue wire with ignition on the (no) charge light should be on, if you connect the blue wire to battery voltage the (no) charge light should go out and the bulb test should end. You can get a replacement regulator - not too expensive.

Alan

CliffH

My alternator died recently. One thing I remember noticing just before was the rev counter needle flicking right up like yours when starting the engine.
I am certainly no expert but think I read somewhere that it can be a sign of failure.

concor

Hi guys, thank you so much for your suggestions!

No, the 3 amp current leak stays after disconnecting the 14 pin connector under the hood. Thanks for the tip though!

Unfortunately that didn't work neither. I still have the 3A current leak after I disconnected the round 10(?) pin connector from the ignition switch below the dashboard. Thx though.



I really appreciate the suggestions, any other ideas? Pleeease?

Mrmerlin

remove the alternator and have it tested

Alan

It seems almost certain to be be alternator regulator - it can have a fault (30) -> ground that will manifest all the time...

Alan

concor

Problem found! It is indeed the voltage regulator or the alternator itself! I removed it and the current leak is gone! So thank you Alan and Mrmerling; you guys were right on the money! I made a little video showing the test:

Next up is to figure out how to test the voltage regulator.

Alan

I'd say it is 99% certain it is the regulator and nothing else causing the extra parasitic leakage - so rather than try to test it (difficult) just get a replacement regulator. The alternator may possibly have other issues too - but it has this one for sure - and a new regulator should cure this leakage (and it gets you a new set of slip ring brushes which is the next most likely issue anyway). So - this most likely solves your current alternator issues.

Alan

CliffH

My 83 also in ruby red recently died while driving due to the alternator failing (exactly same model as yours)
Ended up sending mine away for reconditioning. He changed just about everything in the end, rotor, regulator, bearings and rectifier all for £240 has been spot on since going back on the car.

concor

I had a better look at it and there are two issues. One of the six round diodes is burned and one of the three solder points is broken. Please have look at the video as it shows what I mean

Now I have to figure out how to fix this. Any suggestions please? Cause I'm no expert. At all!

@Alan. Thank you for thinking along, you did point me to the alternator after all. Do you think the voltage regulator is broken as well? Or could this burned out diode cause the 3A current leakage?

SwayBar

If it were me, I'd buy a brand new alternator, install it, and fix the old one afterwards.

Or, have the current one professionally rebuilt.

Alan

A shorted diode could cause leakage from (30) Battery to (31) Ground, but you now need an alternator shop to do the repairs - these are getting few & far between with factory reconditioning (newer types) or replacement being the usual remedy these days. See if there is a well regarded old school automotive repair shop near you. The regulator could still be toast, and a shop will likely suggest a full refresh: regulator w/ slip rings, replacing bearings and a full rectifier replacement too in order to have any warranty - so see if the expense is still a good value.

Alan

Mrmerlin

if you do get it rebuilt then make sure they use a new Bosch voltage regulator,
(and your slip rings will probably need to be renewed.)
any other brand of VR dramatically increases the chances you will be doing the job in the near future.

stay away from using a battery boost box, as these can damage the diodes,
stick with a 6 amp battery charger.
if the battery is low charge it before you put the car back in service ,
dont rely on the alternator to recharge a low battery.
I suggest you find a quality Bosch re manufactured alternator give them your core