Citroen XM Forum

Does the light come on properly or glow faintly and is its lighting predictable all the time?, I know where the loom runs for that feed to the dash display but it might be some other issue

I haven't noticed too much of a pattern so far. I will try to be a bit more scientific this weekend. It is properly illuminated through and either on or off.

Rob

I've not had much cause to look into how an alternator is wired myself, others here are good at it, I would guess the light is there to detect lack of charge and I'm not sure how it could be illuminated in an overcharge situation, as a first stop I would check the two connection are clean and tight on the alternator along with your battery terminals ( if they are the crimped lead type be very suspicious) other than that engine earth strap, I take it its pushing out 14.4v at the battery, engine running, and you don't get dash lighting getting brighter with engine revs. Any oil leaks on the alternator? Battery not going flat?
Could just be one of those really annoying non existent faults.......the type you can never track down.

D

There is no overcharge warning. The light works by feeding +12v to the regulator, which is shunted to Gnd when not charging.

Look at the earth, brushes or regulator for this type of fault.

The dash IGN warning light is connected across the alternator (the single small cable running from the alt), and finally to the IGN switch. IGN sw, when on, will output battery voltage, and so if the alternator is giving a good output, both ends of the warning lamp will be at battery voltage, so the lamp will not light. If alternator output is low or zero, the lamp will glimmer or light.

The dash lamp also has a shunt resistor across it (in parallel with the lamp), to provide the altenator with a feed, from the IGN sw, to "sense" (measure) the battery voltage. The resistor is there so this function will still work in the event of the dash lamp filament breaking.

Try putting a voltmeter between the IGN sw (warning lamp connection) and the small wire connection to the alternator, with engine running at 1500rpm+. There should be no appreciable voltage shown, and the dash warning light should be out.

Apart from checking things out, be aware that there are plenty of sub-standard aftermarket alternators about, sometimes rebuilt to indifferent standards.

Sorted. Stick to the simple solutions! All the alternator connections were good but the battery earth clamp slipped off when twisted. Full marks to Dean,

Wouldn't tighten so I resorted to inserting a small self tapper into the gap. Hey presto no more light on the dashboard.

I think I have a replacement clamp in the stock pile.

Took the car out today and she ran like a dream. No photos as she is filthy.

Rob

Good news.

cxprestigeauto wrote: Took the car out today and she ran like a dream. No photos as she is filthy.

I'm convinced that pretty well all the issues with these cars are down to small, simple bits of maintenance and repair. They are over 20 years old, so need a bit of bringing back to life.

The altinator warning lamp on KBan Sd td i got was always dim when ignition on. Car still charged but the lamp was dim with engine stopped... then i noticed it had gone out completely key on or not.. a quick look revealed a loose 8mm nut on the warning lamp post on the altinator.. tightened it up and the lamp is brighter now and a nice 14.4v charge.

Off to meet up with Dean tomorrow evening at Chieveley services on the M4 to do a little illicit swapping of XM contraband!!

Set of early black leather door cards for a steelie wheel and slightly tired disc hubcap.

Hoping to do the run in the XM but the scaffolders have been busy at Mother's house. It is possible to get the XM down the side alley but it is literally 1" clearance on either side so rather nerve wracking.

Rob