I don’t know if you have this or not, but this will help or not.
Symbols TOC
Power circuit
Grounding Points
Connection locations
Thanks Mark, l didn’t have the connection points as in your post. It will
give me something to look for.
Col
Thanks I’ll try that and post later today.
Col
What was your former profession Carl? I like your analysis. Break the project into pieces, then attack one at a time. Me, I’m a computer systems analyst, by day spanner wielding goon by night. 
No that just illuminates the alternator light and if you earth it the same will happen
Can’t see what conclusions we can come to…the wire from alternator disconnected and test light to that terminal and earth …no light at idle until revs rise slightly and the light stays on.
Conclusion…there is voltage being generated by the alternator to warning light terminal which as I understand it is what should happen. +v at warning light which is cancelled out when alternator volts reach 8 or so volts
No to try an bridge out the wire between the alternator and the dash light
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To clarify, Col; the ign key is connected to the battery and lamp at one end - the lamp is connected to the alternator at the other end. With ign ‘on’, the lamp gets 12V from the ign key and is grounded in the alternator by the brown/black - and is lit. With the alternator producing voltage, turning; the correct alt terminal delivers ‘12V’ to the lamp, countering the 12V from the ign key - lamp is dark…
It’s a simple set-up, but depends on the ‘same’ voltage at both lamp terminals to keep the lamp dark. If there is a voltage difference at the lamp terminals, the lamp may glow weakly - it’s fully lit only when one lamp terminal is grounded…
The lamp only respond to voltages - it does not indicate charging currents; the lamp only needs very low current to light…
Frank
xj6 85 Sov Europe (UK/NZ)
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Thanks Frank, that’s what I had gleamed for tests and other posts.
Therefore there must be a problem between the alternator/ battery light and
the battery. After the exhaust centre to fix a leak tomorrow I am going to
either pull the lamp out a run external wire back to the alternator or see
an auto electrician again. … more to come
Col
Col,
Take a test lamp and connect one end to the battery.
Connect the other end to the Alt.
Start engine and see which terminal does indeed extinguish the light.
Mind you that the Bat light serves also as an exciter voltage for the Alt.
So every time you try a new terminal you should turn the engine of, reconnect and try a different terminal.
If you establish that the Alt works as it should , then the fault must be in your car’s wiring, and as you can see from the schematics Mark posted, a pretty simple one.
Aristides
Aristides1 https://forums.jag-lovers.com/u/aristides1 Aristides Balanos
https://forums.jag-lovers.com/u/aristides1
January 29Frank_Andersen:
To clarify, Col; the ign key is connected to the battery and lamp at one
end - the lamp is connected to the alternator at the other end. With ign
‘on’, the lamp gets 12V from the ign key and is grounded in the alternator
by the brown/black - and is lit. With the alternator producing voltage,
turning; the correct alt terminal delivers ‘12V’ to the lamp, countering
the 12V from the ign key - lamp is dark…Col,
Take a test lamp and connect one end to the battery.
Connect the other end to the Alt.
Start engine and see which terminal does indeed extinguish the light.Mind you that the Bat light serves also as an exciter voltage for the Alt.
So every time you try a new terminal you should turn the engine of,
reconnect and try a different terminal.If you establish that the Alt works as it should , then the fault must be
in your car’s wiring, and as you can see from the schematics Mark posted, a
pretty simple one.Aristides
Thanks Aristides, I am still waiting to hear back from the supplier
again but Battery+ , big terminal and W+(warning light) are the only two
terminals that I was told to use . Surely even I couldn’t mix that up and
as you said the fault must be in the cars wiring and the only place it can
be is the wire from the alternator to warning light. Tomorrow is a new day!
Col
I agree with this gent, this is the next test,
disconnect the wire from alt to light and the test light will BE the warning light, eliminating or indicating wiring
easier than getting at the warning light from behind, on earlier XJ, that can be done fairly easy, not sure on S3
The black s3 cover can be pulled off and then the whole warning light cluster is attached with four screws including a small length of cable that goes to the wiring connector. I would start by measuring the wiring from there and then run the test lamp. One side is always at +12 and the other is 0 when off and -12 when running. To be at 0 (or 8, so probably voltage drop?) it‘ll have to go somewhere at least so it might be the cable rubbing to ground intermittently?
David
Mark:
I completed my army service in 1952, and having acquired a wife and then a child, it was time for me to get a job and support us. I found three choices One, the one I selected, was as an entry level Insurance adjuster. I spent the next fifty years in that profession a t various levels. The last 20 as an independent. Now retired, I merely amplify my DIY stuff. I’ve enjoyed tools since my teen years.
Carl
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you could also use a jumper wire to test. don’t rule out the ignition switch itself! I would add a ground in a few places too. had a similar issue I chased for monthes, eventually added a second ground from engine to frame and problem went away!
Well, finally found the problem. Supplier sent an alternator with different connections. So I rang and asked which terminals to use. Sounds simple! Take the spade connections off the old Lucas and put them on the large post marked +. Connect the two wires that go back to the battery,via , the bulkhead bolt. Done. Now he said connect the terminal from the the old Lucas alternator to the post marked W+. Connect the wire that goes back to the ignition light to terminal W+. Bob’s your uncle! But as the rest of my post says the ignition light stayed on.
Guess what, as there was no diagram from the manufacturer I got lost in wiring and testing. So W+ is the centre of the stator which is used for tachometer on other cars. Only ever produces 8v or so.
Moved the light lead to another spade ( not marked but next to the two ilarge spade terminals in the “plug”) and all is right with the world.
I must thanks all that have offered solutions and help and hope this post might help someone else in the future.
PS. Tightened and welded the muffler leak and have finally got registration certificate for the next twelve months.
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That is awesome! Good work and diligence. Welcome to Jaguar cars!
Cheers!
Now I can sleep tonight! Lol
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