Alternator warning light on with no keys in ignition? Help:)

Alberto18 · 19 Jan 2020

Hi Guys we are new to the forum so thanks for letting us join. We have a 1996 993 C2S

Can anyone help we have a problem with our alternator warning light.

The red alternator warning light on the dash clock is on all the time - bizarrely when no key is in the ignition.

When you put the key in the ignition and turn it one click the red light goes out.
When you start the engine the red light is still out.

Turn the engine off and the light is on.

We have replaced the battery with a brand new one and checked the current at the battery with a multi meter plus putting it under load. Here's the results.

Ignition on engine not started 12.2v

Engine started reading after 30 seconds ish 13.8v

Engine held at 3000 revs reading after 30 seconds ish 14.3v

Fan and lights turned on started at idle 13.2v and went down to 12.3v after thirty seconds

Then fan and lights at 3000 revs 13.2v after this at idle it was 13v.

We have had the clock checked in another 993 and the problem isn't the clock.

Has anyone come across this problem? Any advice on what might the problem be would be greatly welcomed.

Many thanks for your help

Elizabeth

Endoman · 19 Jan 2020

A little worrying because it means the ignition circuit is getting a live feed when it shouldn't. Has it had the loom recall ?(not sure if it's relevant).
Recent electrical work wrongly reconnected?
I would disconnect battery when parked up and get it to an autoelectrician pronto.

kurlykris · 19 Jan 2020

Sounds to me like one of the diodes in the alternator has failed, this will allow current to flow through it in the wrong direction and let power from the battery through to power the lamp :grin:

It is possible to change the doide pack and/or voltage regulator on most alternators yourself, depending how handy you are with spanners :thumb:

The other clue is the alternator output voltages you have measured are too low when fan and lights are on with the engine running at tickover, it should still be over 14v on a good alternator :sad:

Luddite · 21 Jan 2020

Faild diode works for me but you could contact this chap as a renown expert on Porsche electronics and supplier of spares..

https://www.bergvillfx.com/

Look forward to reading how you resolve the issue..

Cameltoe &amp; Heel · 24 Jan 2020

Yeh it could be a diode in the alternator rectifier, I replaced mine recently.

They look like this, you can see the 8 diodes:

Circuit is something like:

Trev

andrewhite · 20 Sep 2022

After the ignition is turned on, there is no charge, and all devices are working. The control signal lamp does not light up. The check is simple - remove the wires from the sixty-one terminal of the generator and connect it directly to the minus (car body). For convenient work here, you will need a flashlight. If the light comes on, the cause of the problems is the excitation winding of the generator. The second option is a bad contact in the connector. If there is no result after stripping, the lamp itself is at risk of burning out. When the key is turned in the ignition, the charge lamp is on, and it continues to twist after cranking.

Trantorman · 20 Sep 2022

if you haven't already disconnect the battery, when you're not with the car, the most likely cause is the alternator, but as others have said it could be a failed engine wiring loom, so better to be safe than sorry.

Alternator warning light on with no keys in ignition? Help:)

Alberto18

New member

Endoman

Albert Park

kurlykris

Singapore

Luddite

Indianapolis

Cameltoe & Heel

Barcelona

andrewhite

New member

Trantorman

Nurburgring

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