Ign/Charge Light spontaneously reversed?

K

karekare

New Member
Hello All,
Hoping someone out there can offer some worthwhile suggestion on this one! I've searched the forums, and whilst there is plenty of the usual Charge light issues- (Alternator trouble or snapped/loose belt) this one seems a first-aside from the guy who's brother put a battery in reverse polarity frying the Stereo-which is definitely not the case here.

Car is a '74 P6B Auto. Up until last night, the Charge Light would work as expected, being, it would Come on with the Key, Go out once engine running, but begin to glow faintly at prolonged idle (approx 600rpm), going out as soon as the car got to 900/1000rpm. No issues with charging.

Last night, when I parked the car briefly & removed the Key, the Ignition Light stayed on Brightly-although, after driving, this light now goes out when car "off" key removed.
When the Key is put in, and turned to the position immediately prior to engaging the Starter motor, the Light illuminates,
Once the motor starts, when driving, (RPM in the usual 1500-2500 sort of range) the Ign lamp glows brightly, getting brighter as the charge increases, and dimming off around 1000rpm, but glowing to a lesser degree again around 600rpm.
Clearly the lamp is responding to information from the Alternator in that the brightness is directly related to engine speed.

I am no Auto Electrician, but put a Multimeter on the Alternator. around 2500rpm its putting out 15.4v, so is charging. I also tried it at the Battery, 12.7v engine off, and in the 15's once the rev's come up.

As I said, I'm really no Auto Electrician, Any ideas would be much appreciated, surely I'm not the first?

regards,

Sean
 
I suspect the internal regulator is suspect, the alternator should not be putting out 15.4 Volts 14.4 to a max of 15 would be what I would expect.

Graeme
 
There should be a single small wire going into the back of the alternator, possibly brown with a black tracer.

With the ignition on, remove this wire, careful not to touch anyhting with it as it should be live. Put your multimeter into the end of the wire. It should be 12V more or less. If it isn't then your have a wiring fault to this spade.

Then check the spade it fits onto.

That should be 0V. If it is 12V then you have an alternator fault.

I had this once so know this bit, it could probably be a lot more complicated than this though :?

Richar
 
Hello Sean,

I agree with Graeme in that the voltage regulator within the alternator is almost certainly the culprit. With that sort of voltage appearing across the battery when the engine is running, damage to the battery will occur as it is being very much over charged. Usually a maximum in the order of 14.5V could appear across the battery, but certainly no more.

You can either buy and fit a new voltage regulator which is not a diffucult job or allow an auto electrician to do it for you for a much greater fee.

Ron.
 
SydneyRoverP6B said:
Hello Sean,

I agree with Graeme in that the voltage regulator within the alternator is almost certainly the culprit. With that sort of voltage appearing across the battery when the engine is running, damage to the battery will occur as it is being very much over charged. Usually a maximum in the order of 14.5V could appear across the battery, but certainly no more.

You can either buy and fit a new voltage regulator which is not a diffucult job or allow an auto electrician to do it for you for a much greater fee.

Ron.
Click to expand...

TBH, I'd get it checked by a professional. As necpwa says (and if I've interpreted properly!), it may be one of the main rectifier diodes. The replacement reg, in that case, could easily go the same way!
 
necpwa wrote,...
It's a diode in the alternator that has failed and probably taken the reg with it.
Click to expand...

That is a possibility too. When one or more of the diodes within the bridge fails, from what I have seen the ign light will be illuminated at idle, and then as the engine revs increase so the intensity of the glow will diminish until it fades out completely.

Still,...anything is possible.

Ron.
 
I have a similar problem with mine! its ok for a while and then the light comes on, then it goes off and i have charge again. This happens on every journey.

I suspected it was the regulator, Is this a seperate unit on a V8? If so where is it located?

Thanks,
Aaron.
 
Its located in the Alternator with the ACR Alternators.
With mine the Alterntor light wont go out till its past idle and comes back on again at slow idle, maybe I should take it apart and check for dodgy Diodes, thought it does not seem to present any charging issues but then again the car battery is always on as solar panel when it's parked in the garage so is always charged.

Graeme
 
The Rovering Member said:
http://cgi.ebay.co.uk/LUCAS-15-16-17-18-ACR-REPAIR-PARTS-KIT-LRA100-101-ETC-/310201740368?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item483976ec50

Nothing to do with me but they're one of our local businesses.
Click to expand...

I don't even have to click the link to know who that is..........
 
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