Alternator help, charge light

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fergus123

fergus123

Active Member
Posts
153
Need some help here, I have just fit a 200tdi from a disco into a series 2a,


I have wired the alternator so that the two brown wires go onto the battery via the starter motor. Then the brown and yellow tract small wire goes up into the bulk head.

When the battery was connected and the isolator was on; the charge light came on, and when ignition was switched on the charge light would go out. I have had this problem before on the old engine and replacing the alternator fixed it.

I had a spare Lucas a127 which was from a transit it was only used for about a weak and removed as an oil seal went on it with vacuum pump, and working when taken off about 4 months ago, it has been sitting dry, and when this was fitted; wired in the same way as the old one, the charge light would come on when ignition on and stay on when the engine was started and revved.

Is there a way to check the alternator is working or are these the signs that the alternator is dead.

Any advice welcome.
 
Do you have a volt meter? If so pot it on the battery with the engine not running it should read about 12.7 volts and around 14 volts with the engine running if everything is ok.
 
Okay, could it be that the alternator is not "exciting"? , I will get the multimeter on it tomorrow.
 
could verry well be a break in the wire where it goes towards the bulkhead past the manifolds ( the heat makes the wires brittle )
 
everything was working before the conversion, started it for second time today. I recon it is the alternator, but don't want to order a new one unless I have to.

i guess ill check over the trace wire.
 
You need a +12V supply to the charge lamp from the ignition switch, the other side (-ive side from the lamp) goes from the lamp to the small terminal on the alternator.
 
Okay, Had volt meter on it today, I had 12.7v when running and when off. When ignition was on I had 6v coming into charge light, so assume there is a diode gone, I tried replacing the brushes/ voltage regulator pack with an older one, but no luck.

I have three broken alternators so I am taking them all to my auto electrician and he will give me one working on in return/ get one running. Seems like a good deal!
 
Just got back from the auto electrician, The alternator checked out okay, what could be the problem, the charge light is giving 6 volts? as if it is not charging or something. Could it be a bad ground? or a poor connection from the alternator to the battery?
 
Daft question, but what size lamp have you got in your charge warning light?

It should be 5W, anything higher would reduce the power to the exciter coil.

Check your earths between the block and chassis, block and battery, battery and chassis.

Also check your +ive connections from your battery to the starter and from the battery to the alternator.
 
fergus123 said:
Need some help here, I have just fit a 200tdi from a disco into a series 2a,


I have wired the alternator so that the two brown wires go onto the battery via the starter motor. Then the brown and yellow tract small wire goes up into the bulk head.

When the battery was connected and the isolator was on; the charge light came on, and when ignition was switched on the charge light would go out. I have had this problem before on the old engine and replacing the alternator fixed it.

I had a spare Lucas a127 which was from a transit it was only used for about a weak and removed as an oil seal went on it with vacuum pump, and working when taken off about 4 months ago, it has been sitting dry, and when this was fitted; wired in the same way as the old one, the charge light would come on when ignition on and stay on when the engine was started and revved.

Is there a way to check the alternator is working or are these the signs that the alternator is dead.

Any advice welcome.
Click to expand...

fergus123 said:
Okay, Had volt meter on it today, I had 12.7v when running and when off. When ignition was on I had 6v coming into charge light, so assume there is a diode gone, I tried replacing the brushes/ voltage regulator pack with an older one, but no luck.

I have three broken alternators so I am taking them all to my auto electrician and he will give me one working on in return/ get one running. Seems like a good deal!
Click to expand...

fergus123 said:
Just got back from the auto electrician, The alternator checked out okay, what could be the problem, the charge light is giving 6 volts? as if it is not charging or something. Could it be a bad ground? or a poor connection from the alternator to the battery?
Click to expand...

your bat is on and you turn you ign on. the alt light turns on as current is sent down via the bulb to the alts field coil and then it earths. If the bulb is not on then either bulb is blown, it has no power, you've stuck the wires on wrong or it is not being earthed on the alt.

first off i'd make sure you added a good earth strap between the engine and chassis, then recheck the wires are plugged into the alt correctly.

if the batt is on, ign off but the charge light is on, then the bulb is getting power somehow. stick a multimeter on the bulbs wire on the side coming from the alt, is that supplying the power? If so, then i'd check your wiring. ie check where you plugged the wires into the alt, not that they just fit.

fyi, when the alt is running, it switches from ground to 12v which equalises the current from your dash and puts the lamp out.

maybe take a pic of your wiring
 
Last edited:
Which alternator is it 200tdi one has a W connection which is rev counter as well as dash light / excitation one\
Alternator 200tdi.jpg
 
alternator is wired correctly, when charge light wire is put to ground the bulb lights brightly. I had mechanic over and we came to conclusion that it was due to a poor ground.

Alternator charges when excited manually from battery.

Once I have the exhaust finished and seat box installed I will go ahead and install a new earth strap to one of the studs on the gear box and also a braided strap onto the chassis from the block.

Charge lamp bulb is a 2.2w as far as I can see.


Will update tomorrow once battery is in a more permanent place.
 
trax said:
your bat is on and you turn you ign on. the alt light turns on as current is sent down via the bulb to the alts field coil and then it earths. If the bulb is not on then either bulb is blown, it has no power, you've stuck the wires on wrong or it is not being earthed on the alt.

first off i'd make sure you added a good earth strap between the engine and chassis, then recheck the wires are plugged into the alt correctly.

if the batt is on, ign off but the charge light is on, then the bulb is getting power somehow. stick a multimeter on the bulbs wire on the side coming from the alt, is that supplying the power? If so, then i'd check your wiring. ie check where you plugged the wires into the alt, not that they just fit.

fyi, when the alt is running, it switches from ground to 12v which equalises the current from your dash and puts the lamp out.

maybe take a pic of your wiring
Click to expand...

Ran through all charge light wiring from wiring diagram drawn by auto electrician today, all seems correct, and tested resistance of wires, all seem okay, the bulb lights okay when charge light is grounded. I think there is a problem with the ground somewhere. Will check tomorrow.
 
redid ground wires, still not luck, manually exciting the alternator seems by jumping the terminals seems to start it charging for a while.

I have checked all the other wiring and it is okay, really confused about this now.
 
trax said:
if the batt is on, ign off but the charge light is on, then the bulb is getting power somehow. stick a multimeter on the bulbs wire on the side coming from the alt, is that supplying the power?
Click to expand...

did you do that?

it sounds like the alt is chucking up 12v to your dash all the time, then when the ign is on and it sends 12v down, they cancel each other and turn the light off.

sounds like a broken alt to me, possible short.

an alt is an electromagnet, turn ign off, battery connected and see if the alt is magnetised by sticking something steel on it. discon bat and see if it still sticks.
 
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