dickster Posted May 30, 2009 Posted May 30, 2009 (edited) i am no electrical expert, so here's the issue. my alternator warning light does not come at all but when i turn the ignition on i get 12v at the bulb holder - i have tested the bulb and its fine! is this possible, to have 12v going to the bulb and no illuminated light bulb?! i have tried a couple of bulbs. i have also tried connecting the spades directly onto the bulbs. i am pretty sure that the alternator needs replacing (no charging voltage) but i need to clear up this odd issue first. cheers rich ps posted on pelican too http://forums.pelicanparts.com/showthread.php?t=477207 Edited May 30, 2009 by dickster
dickster Posted May 30, 2009 Author Posted May 30, 2009 (edited) Is the bulb holder earthing OK? hello john, i dont know, i just checked and got 12v so thought everything should be ok? Edited May 30, 2009 by dickster
johndglynn Posted May 30, 2009 Posted May 30, 2009 i dont know, i just checked and got 12v so thought everything should be ok? It needs an earth to work mate. If you clip a voltage tester to a live source, touching it off the body of the bulbholder should light it, thereby showing earth.
dickster Posted May 30, 2009 Author Posted May 30, 2009 It needs an earth to work mate. If you clip a voltage tester to a live source, touching it off the body of the bulbholder should light it, thereby showing earth. just to be clear then, even though i get a reading of 12v with the meter, there still may be an earth fault? i'll try as you have suggested.... thanks
johndglynn Posted May 30, 2009 Posted May 30, 2009 just to be clear then, even though i get a reading of 12v with the meter, there still may be an earth fault? Yes mate. Current flows through an in and an out: a positive and a negative. You have the plus, do you have the minus is the q.
pete917 Posted May 30, 2009 Posted May 30, 2009 12v always has to find its way to earth..... When you tested the supply where did you put the neg lead from the ameter?
dickster Posted May 31, 2009 Author Posted May 31, 2009 (edited) i just connected the meter leads to the two leads going to the bulb holder - i guess its not as simple as that. as i said, electrics are not my thing! note - the first time i did it, i got -12v, then i swapped the leads around and got +12v? Edited May 31, 2009 by dickster
dickster Posted May 31, 2009 Author Posted May 31, 2009 ok, i connected + to permanent source and tested the blue wire for ground - it worked fine with ign on or off. i still dont understand why the bulb doesn't light!
johndglynn Posted May 31, 2009 Posted May 31, 2009 ok, i connected + to permanent source and tested the blue wire for ground - it worked fine with ign on or off. What blue wire? The bulb earths through the bulb holder, did you test that? Is there maybe a bit of corrosion on the positive contact in the holder? Make sure the contact and the body of the bulb are shiny bright.
pete917 Posted May 31, 2009 Posted May 31, 2009 note - the first time i did it, i got -12v, then i swapped the leads around and got +12v? Don't worry too much about the sign. You need to make sure your black lead from your meter is connected to the ground side of the circuit, then you'll get your +12v. Do a continuit test from the case of the gauge to a known good earth. Just to make sure. The brown lead to the case is the earth so check that too to a good earth. Check that the connector is clean and not corroded. If necessary give it a clean with some emmery paper.
dickster Posted May 31, 2009 Author Posted May 31, 2009 (edited) What blue wire? The bulb earths through the bulb holder, did you test that? Is there maybe a bit of corrosion on the positive contact in the holder? Make sure the contact and the body of the bulb are shiny bright. just had another go (been out all day). when you say the bulb earths through the bulb holder, the bulb holder is plastic and the blue wire provides negative (or earth?) from the alternator? the other wire is positive and provides current on ignition. here's how it just went. 1. connected both wires back on bulb holder and bulb back in. turn on ignition and bulb lights up! start engine bulb goes out. check volts at battery and get 16.9v - way too high and points to regulator? 2. turn off engine and tried again, this time no luck and bulb does not light up. 3. took blue wire off bulb holder and earthed bulb hohoer via back of gauge - bulb lights up. 4. then i tried voltmeter on positive side of battery and negative lead to blue wire - 12volts! independently then the two wires going to the bulb holder seem to work fine, just not together! i'll see if i can get a bulb to light up with a different positive feed using the blue wire for earth....... *edit* using a positive feed direct from the battery and using the blue wire (actually blue/red) the bulb will still not light up but i do get 12v?!! bentley manual says to disconnect the blue wire from the alternator and touch to ground to see if bulb lights - if it does fault lies at the alternator end. i'll try that on tuesday....... Edited May 31, 2009 by dickster
johndglynn Posted May 31, 2009 Posted May 31, 2009 All my earths are brown and no bulb works without an earth so gonna have to look at a diagram.
dickster Posted May 31, 2009 Author Posted May 31, 2009 (edited) All my earths are brown and no bulb works without an earth so gonna have to look at a diagram. John, Maybe my '86 is different (i think pete is refering to an older model as well)? The bulb holder is plastic and insulated from the gauges so cannot be earthed in that way. The bentley manual shows (in diagram) the blue/red wire going through the alternator to ground. The other wire going to the holder is a positive feed "live" on ignition. I'll test the blue as the bentley suggests but i think the alternator or regulator are at fault - given that i got nearly 17v at the battery today. Edited May 31, 2009 by dickster
johndglynn Posted May 31, 2009 Posted May 31, 2009 i think the alternator or regulator are at fault - given that i got nearly 17v at the battery today. Oh yes mate, knackered.
dickster Posted June 2, 2009 Author Posted June 2, 2009 I had a chance to get to the alternator wires today. There is indeed a blue wire on the back of the alternator, together with red (back to battery positive) and brown (earth). The blue wire checked out okay so given that I got nearly 17v at the battery a day or so ago I decided to leave the alternator and put in a new regulator (the brushes looked very worn). Bingo, warning light is functioning as it should and after bolting everything back up I now have a healthy 14.4v at the battery with the engine running. A voltmeter would be a useful gauge to have.... Rich
siggy Posted June 2, 2009 Posted June 2, 2009 Just so happens that mine broke down on the way to Gaydon, on Sunday. Started running rough and I pulled over, would not even crank over. Ignition warning light lit as it should. Got it recovered and checked it out. When I tried at home no ignition light, bulb OK live to the bulb but no continuity in the wire to the alt. Removed the alt and earthed the blue wire out still no light so faulty alternator.
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