crabmaster
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Attribute: http://www.austineighteenhundred.com.au
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Post by crabmaster on Mar 2, 2016 9:47:10 GMT
One side of the warning light bulb goes to +12V (white wire). The BRY wire goes to the alternator which, when the engine is not running, is at earth potential, and so the bulb lights. When the engine is running, the alternator provides voltage to the BRY wire, and so the bulb has +12V coming from both sides, and so the light goes out. If the output from the alternator drops a little below battery voltage (say because low idle speed), the bulb has a small potential across it and so glows weakly. Tony
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cbv8
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Post by cbv8 on Mar 2, 2016 10:21:33 GMT
Hi Tony, Thank you for the info i actually understand that but what i don't understand is how i have a +12v feed through the white wire when i earth the b/y wire but nothing when its not earthed? Does this as many people have said mean a break in a wire or a wire come off the alt? i am going to attempt to get to the alt wires today but i looks hidden away  |
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crabmaster
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Attribute: http://www.austineighteenhundred.com.au
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Post by crabmaster on Mar 2, 2016 11:57:51 GMT
Not sure what you mean by the terms "feed" and "nothing".
Do you mean "voltage measured at the white wire"?
With the engine not running, if the BRY wire is not connected to the alternator because of a break or poor connection at the alternator (or control box), or you holding it in your hand, then the light will never come on. If you hold the BRY to earth, the light should come on since then there is a circuit and current flows through lamp through from the white wire.
By the sound of it, your problem is probably in the regulator control box (or internal regulator on the back of the alternator) - but I am not sure what type of alternator is fitted to UK cars. (In Australia, there is a small regulator control box mounted in the same place as the older generator regulator relay unit). Inside this box is a mechanical relay which switches in the earth connection when there is no alternator output. This relay may give trouble. Some alternators have a built in regulator that performs the same task.
Note, if the relay is stuck open, the light will not come on, and the alternator may not excite and produce charge.
Tony
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cbv8
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Posts: 33
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Post by cbv8 on Mar 2, 2016 16:48:20 GMT
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Post by Penguin45 on Mar 2, 2016 23:58:24 GMT
Thanks Tony - that was the explanation that I was unable to explain.... Dead easy, getting the alternator off - try a Daewoo Matiz if you really like a challenge.  No, don't - a gallon of petrol and a box of matches is much simpler. Chris. |
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No, don't - a gallon of petrol and a box of matches is much simpler.