S3 charging/alternator concerns

[muz122]

Hi chaps, hope everyone is ok.
After finally sorting out running issues (I'll update that thread shortly), on first test drive the ignition light came on and battery voltage on the voltmeter was in the red.
Checked voltage with multimeter across the battery terminals = 12.xx and gradually falling. I noticed the red warning light below the oil pressure light was also illuminated. After increasing RPM to around 1500, I was getting over 13V but ignition light still on. That's as much as I did that day as it was getting late.
Next day, started up, ignition light on and charging at idle. The red light below oil pressure light not on.

Spent a couple of days searching posts here, analysing wiring diagrams and workshop manual to no avail unfortunately. Looking at my pictures, can anyone identify if the alternator looks original? Workshop manual and other posts suggesting there should be a voltage regulator near the battery....there isn't one on this car!
There are 2 terminals on the alternator. One terminal has a small blue wire (exciter maybe?). I noticed that when the concern is present, there is ~1.5V here. When no concern, charging voltage is present. Both belts are tight as are alternator connections and main engine earth strap.
So, my main questions:
1. Does the alternator seem original?
2. Are there any other installation locations for the voltage regualtor? Or, could it not have one?
3. Is that blue wire the alternator feed/exciter?
4. What is the red light below the oil pressure light?








Many thanks in advance,
Matt

[angelw]

Hello Matt,
The Alternator is Not original equipment; the original alternator was a B.U.T.E.C.

The B.U.T.E.C. alternator has three wires connected. One to the battery, one to the ignition warning light (via the regulator) and one to the regulator.

With the absence of an external regulator on your car, the regulator will be built into the alternator fitted. Of the two wires connected to your alternator, one would go to the battery, and the other to the Ignition Warning Light. 12v on that wire would be required to extinguish the Ignition Warning Light.

The light below the Oil Pressure Warning light is the Brake Fluid Level and Hand Brake Warning light and it's illumination is coincidental with the issue you're having with the alternator. However, you should check the level in the two brake reservoirs and ensure that the Handbrake in not partially on and that the switch for the Handbrake Warning is operating correctly.

Regards,

Bill

[MarekH]

There is a wiring diagram in the electrical section of the manual - that's the big blue and black book you need to have a copy of. You can also find a copy of the wiring diagram on xkedata.com or in the knowledge base.

You look as though you have an ordinary aftermarket alternator which is typically a "single wire" alternator, so called because its regulator control box already sits inside the alternator. The single wire is to the ignition light on the dash and will be linked to the car's brown/black wire which can be seen at the old regulator connection under the right hand bonnet latch.

Do not confuse it with the oil pressure warning light behind the dash which has similar colours but comes out at the oil pressure switch attached to the engine block.

You sound like you have an alternator charging problem as it should read 14 to 14.4v with engine running.

kind regards
Marek

[muz122]

Thanks Bill and Marek,
Sent the alternator off for testing/repair locally. Hopefully that's all the issue is. Will update.

Many thanks,
Matt