What have I done????

[SteveS]

I hope some of you electrical gurus can help me out on a problem that I have just got. The other day I was looking at the petrol tank (I had a smell of petrol in the boot) and noticed that one of the wires was not connected to the tank so I put it on. Today I started the Stag, she fired first time and then I drove about 10 miles to town but noticed that the red fuel warning light was on (the tank was full of fuel so I knew this to be erroneous); I then parked up for 10 minutes. On my return to the Stag, I found the battery flat. A really nice guy (who owned a TR6) gave me a jump start and again I drove home but when I turned the engine off, and left the car 10 minutes, the car wouldn't start, although the lights work. Putting a voltmeter across the battery gives 12.29 V. Unplugging the orange and green wire turns the red fuel light off, but doesn't help the starting problem, and taking the black and green wire off, kills the fuel gauge; the other wire to the tank is black. I don't understand what is happening here. Any ideas would be gratefully received
Steve

[jakesmig]

With yor battery showing 12.29v it wasn't flat, after all, your lights still worked, just not responding to instruction. We had this with our rally car yesterday, 3 batteries all 'flat' turned out to be a bad earth
When you jump started the car did you earth to the battery or the engine block? Suonds more like an earthing problem to me than anything associated with the fuel tank leads. look at battery earth, car / body earth, solenoid connection
John

[SteveS]

John,
Thanks for the reply and the advice. I put the earth to the battery but what I don't understand is why this should suddenly occur when everything was fine when I set out.
Steve

[GDPR]

There are two states of vehicle engineering - good and broken - you've just been unable to exactly define the change point......

[SteveS]

I've currently got the Stag up on stands and found my electrical problem; corrosion has caused a thick black insulated wire to fall away from the alternator. Looking at the wiring diagram, I should have a brown/purple wire, a brown/yellow, a brown/purple and a brown wire at the back. Unfortunately I have a a completely different colour scheme (and I'm sure I'm not the first to find this out on Lucas wiring!). Looking up at the alternator from underneath the car, at 11 o'clock I have a green/brown wire, then inside of it I have a brown/green which is inside a square plastic connector; at 2 o'clock I have a yellow/green wire. The wire that has come away is a thick black insulated wire, which I suspect come from the battery.
The big question I have is where does the black wire connect to on the alternator? If someone could please answer this I should be able to fix the problem today
Steve