1997 4.6 HSE No charge light after fitting new alternator

Datatek said:

I agree with you, what I was disputing was your comment about the "little wire usually black" It does not exist on this alternator. the earth is via the electronics in the regulator to the frame of the alternator.

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Ok then, a little wire usually black but on occasion sky blue pink with yellow dots on. Whatever colour it is, that is the charging light earth circuit. With the ignition switched on an earth state is present through this wire via the controller. As current begins to flow the controller opens the circuit and causes the light to go out. Or in the case of a P38 sends a signal to the Becm to switch the light on or off as the case maybe. The Becm does not control charging the alternator controller does, the Becm only controls the dash light, in this case at the request of the alternator controller. So my first statement that in the case of the light not coming on at all and if the wire from w+ is flashed to earth and the light comes on that an earth fault is the problem was correct then? The alternator fault he is getting is the Becm telling him there is no earthed state through the W+ terminal.

wammers said:

Ok then, a little wire usually black but on occasion sky blue pink with yellow dots on. Whatever colour it is, that is the charging light earth circuit. With the ignition switched on an earth state is present through this wire via the controller. As current begins to flow the controller opens the circuit and causes the light to go out. Or in the case of a P38 sends a signal to the Becm to switch the light on or off as the case maybe. The Becm does not control charging the alternator controller does, the Becm only controls the dash light, in this case at the request of the alternator controller. So my first statement that in the case of the light not coming on at all and if the wire from w+ is flashed to earth and the light comes on that an earth fault is the problem was correct then? The alternator fault he is getting is the Becm telling him there is no earthed state through the W+ terminal.

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Sorry to have to say this, but you are talking out of an orifice located somewhere below the waist line.
The circuit does not go open, but the voltage level changes from near earth potential to +12 volts as the alternator begins to charge. Thus before the alternator starts, there is 12 volts from the ignition switched circuit via the charge lamp throught the regulator and roatating field winding to earth which provides the initial excitation current (on the P38 this comes from the BECM but the effect is the same), the earth is internal to the alternator and is effectively the same as the frame. As the alternator starts to charge the level rises to +12 volts thus the charge lamp (or BECM) has 12 volts on both sides which = no current flow so the lamp goes out or in the case of the P38 the BECM sees no current flow and switches the light off. If you don't believe me I suggest you look at page 51 section B1 Starting and Charging, Range Rover Electrical Trouble Shooting Manual
There is no little earth wire for the charge light black or any other fecking colour on a typical alternator just the W+ which may be different colours on different vehicles.
:multiply:

Datatek said:

Sorry to have to say this, but you are talking out of an orifice located somewhere below the waist line.
The circuit does not go open, but the voltage level changes from near earth potential to +12 volts as the alternator begins to charge. Thus before the alternator starts, there is 12 volts from the ignition switched circuit via the charge lamp throught the regulator and roatating field winding to earth which provides the initial excitation current (on the P38 this comes from the BECM but the effect is the same), the earth is internal to the alternator and is effectively the same as the frame. As the alternator starts to charge the level rises to +12 volts thus the charge lamp (or BECM) has 12 volts on both sides which = no current flow so the lamp goes out or in the case of the P38 the BECM sees no current flow and switches the light off. If you don't believe me I suggest you look at page 51 section B1 Starting and Charging, Range Rover Electrical Trouble Shooting Manual
There is no little earth wire for the charge light black or any other fecking colour on a typical alternator just the W+ which may be different colours on different vehicles.
:multiply:

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So it would seem this guy is telling lies when he says he takes the wire from W+ and flashes it to earth the light comes on. You say there is no such wire. The charging light is just the same circuit as any other apart from the fact that it uses the Becm to switch the light instead of doing it directly. Then the only fault can be that there is no earth path through the controller. Why try to make something so easy to understand so bloody difficult with all your mumbo jumbo. There is a fault on the controller plain and simple. If he is getting good volts accross the battery everything else is workig including the exciter circuit otherwise there would be no output. You need to get your hands dirty a little more instead of all that reading.

wammers said:

So it would seem this guy is telling lies when he says he takes the wire from W+ and flashes it to earth the light comes on. You say there is no such wire. The charging light is just the same circuit as any other apart from the fact that it uses the Becm to switch the light instead of doing it directly. Then the only fault can be that there is no earth path through the controller. Why try to make something so easy to understand so bloody difficult with all your mumbo jumbo. There is a fault on the controller plain and simple. If he is getting good volts accross the battery everything else is workig including the exciter circuit otherwise there would be no output. You need to get your hands dirty a little more instead of all that reading.

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You were talking about some non specific little black wire (or sky blue pink with yellow dots) not the W+. How many alternators have you got your hands dirty on re-building? The W+ wire does go to earth but not directly, as I said the earth passes through the regulator and the rotatating field windings of the alternator to the W+. Personally I prefer to study and understand the electrical schematics rather than making guesses as how electrical/electronic systems work.

UPDATE : Yesterday I replaced my inlet manifold gasket and spark plugs lead, once this had been completed I turned the key to ignition 2, no charge light, I started the vehicle and left it to idle for around 20 minutes whilst I cleaned up and put my tools away. I then reversed the car a few feet so I could close the garage door, then drove forward a few feet to park. Turned car off then decided to check it would start, get to position 2 on ignition, notice that the charge light is illuminated, start car, light goes out. I do this 4 or five times just to be sure. No changes made to alternator, or wiring but now light is working as it should. Will be taking the car out for a drive today to check all feels ok and to see if the bulb continues to function correctly. I will update the post with what I find.

Bad earth :behindsofa:

nathan5346 said:

Bad earth :behindsofa:

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Or bad connection

Datatek said:

You were talking about some non specific little black wire (or sky blue pink with yellow dots) not the W+. How many alternators have you got your hands dirty on re-building? The W+ wire does go to earth but not directly, as I said the earth passes through the regulator and the rotatating field windings of the alternator to the W+. Personally I prefer to study and understand the electrical schematics rather than making guesses as how electrical/electronic systems work.

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You may well study them mate but you certainly don't understand them. What other wire is there apart from a bloody great charging cable. What other wire do you think i was talking about. So the W+ wire does go to earth but not directly. That is what i have said all along. The charging lamp will not light unless the 12 volt W+ is directed initially to earth through the controller. That is why i said the lamp not coming on if the bulb is sound is a earthing fault. What colour of wire it is is a sick jumbo. I have been getting my hands dirty for over fourty years. I have repaired many alternators for a few quid that you maybe would have bought a replacement for. Don't try and teach your granny to suck eggs mate it won't work. You try to give the impression there is something difficult about alternators they are pretty basic and simple pieces of kit no black art involved here.

nathan5346 said:

Bad earth :behindsofa:

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Datatek said:

Or bad connection

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No it a P38... fixed until next time by the fairy's at the bottom of the garden.............:bolt:.:behindsofa:

zzr1200 said:

No it a P38... fixed until next time by the fairy's at the bottom of the garden.............:bolt:.:behindsofa:

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That's about the size of it. The bad earth or bad connection or bad connection to earth seems to have resolved itself. If you own a P38 and don't believe in faries at the bottom of the garden you would go nuts pretty quick. They are the only (sometimes) self repairing vehicle i have ever known.

designed by Microsoft?

jdennington said:

UPDATE : Yesterday I replaced my inlet manifold gasket and spark plugs lead, once this had been completed I turned the key to ignition 2, no charge light, I started the vehicle and left it to idle for around 20 minutes whilst I cleaned up and put my tools away. I then reversed the car a few feet so I could close the garage door, then drove forward a few feet to park. Turned car off then decided to check it would start, get to position 2 on ignition, notice that the charge light is illuminated, start car, light goes out. I do this 4 or five times just to be sure. No changes made to alternator, or wiring but now light is working as it should. Will be taking the car out for a drive today to check all feels ok and to see if the bulb continues to function correctly. I will update the post with what I find.

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Then it sounds like the Becm was having a duck fit. If you are getting a charge then the exciter circuit must be working, this under normal circumstances would also turn on the charging lamp. But as it is switched through the Becm so the computor can monitor the system, obviously the Becm has glitched and not turned it on. As i said earlier if the lamp does not come on it is more often than not a earthing fault which would also mean that the exciter windings were not active either. Therfore you would not get a charge, as you did have a charge but the light was still not working it can really only have been a Becm glitch and not the usual earth fault.

Went out for a drive today to test things out, when switching the ignition to 2 there was no charge light, drove 20 miles, stopped, turned back to ignition 2 and there is the charge light working as it should. Left car for an hour, tried again and the charge light was still there. Tried again after several hours, no charge light, it's as though the charge light only illuminates when the alternator is hot, which leads me to think that perhaps there is a dry joint on the alternator side that makes contact as it expands. The battery is getting a good charge so the sytem is working as it should. I have to say a big thank you to everyone who posted replies, especially Derek, Datatek and wammers to name but a few

Cheers J. Glad you're getting somewhere with it and you're confident to use it. I think your diagnosis sounds pretty reasonable. I would tell Britpart your findings. I'm sure they'll do their best to make sure you're a satisfied customer. It's given us some entertaining reading for a day or two anyway!