V8 won't charge

Hi all, I have a 1996 V8i that I have recently changed the engine (the old one may have taken a "small" drink in a deep puddle).
I eventually got her up and running and much faffing and swearing, now the only problem I'm having is the fact she won't give a charge.
The battery light will go out on the dash when the engine is running until the revs increase to around what I guess is 3k, I need to guess, because the rev counter doesn't work either.
Using a multimeter, I've got a resistance of about 50ohms from the body of the alternator to the negative terminal on the battery. I've even tried connecting a jump lead from the engine to the negative with no joy.
I eventually bit the bullet and bought a new alternator though I still have the same problem.
I reckon I've connected all the earths and the wiring from alt to the fusebox to battery would seem to be correct.
I've trawled the internets for hours but can't seem to get anywhere (apart from one person who had the same symptoms as me but never posted how he fixed it!).

Can anyone shed any light? Is my car eating alternators? Will it be something obvious?

Cheers

Lucas

Using a multimeter, I've got a resistance of about 50ohms from the body of the alternator to the negative terminal on the battery.

Surely you mean 0.5 ohms

Hmmm, the multimeter was on the lowest setting which I though was 200ohms. I got a reading of 50, I don't have the car to hand to double check this though.
Using my old analogue meter it showed 0 ohms, though I'm not certain how accurate it is!

Dont measure resistances....check voltage at the alternator terminal with (+) disconnected while the engine is running...if u have voltage there then reconnect + and check again...if u loose power then its a drain somewhere, if not check between earth and the battery + lead (disconnected from battery) ...... if no power then somewhere the circuit is interrupted..... Unfortunately i dont have wiring diagram for disco1 to help u more.

sierrafery said:

Dont measure resistances....check voltage at the alternator terminal with (+) disconnected while the engine is running...if u have voltage there then reconnect + and check again...if u loose power then its a drain somewhere, if not check between earth and the battery + lead (disconnected from battery) ...... if no power then somewhere the circuit is interrupted.....did u check the charger relay so far? Unfortunately i dont have wiring diagram for disco1 to help u more.

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Hi, there's definitely no voltage coming from the alternator. Charger relay? Any ideas where it is/what it does?

No charger relay
Have yu got volts from the warning light circuit?
Does the warning light come on?
Does the warning light go off?

Yup, there's definitely voltage getting to the alt through the bulb and it goes out when started. It does come on again when the revs increase to about 3k though but goes back out when the revs decrease.

Lugy said:

Hi, there's definitely no voltage coming from the alternator. Charger relay? Any ideas where it is/what it does?

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Forget about the charger relay i was thinking to what happened to a friend of mine but he had a split charger relay retrofitted. Sorry

When u say no voltage coming u mean where? > at the alternator's terminal cos if it's so then the alternator is f***ked.

sierrafery said:

Forget about the charger relay i was thinking to what happened to a friend of mine but he had a split charger relay retrofitted. Sorry

When u say no voltage coming u mean where? > at the alternator's terminal cos if it's so then the alternator is f***ked.

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even his new one ?

Lugy said:

I eventually bit the bullet and bought a new alternator though I still have the same problem.

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An update for everyone, after burning my finger on the pulley on the alternator I realise the belts was slipping slightly. The fact that the tensioner was against the stop confirms this. It would seem that the heads on my replacement engine are slightly different.

Any, I've machined up a spacer to raise the alternator by about 25mm which has worked a treat. I'm still getting the same problem though, except now at higher revs the battery light doesn't come on.

Yu cud, of course, get a smaller belt.

People might like to know that it's working now.

I've taken the new alt back to the factors and a new one's coming in tomorrow. In the mean time I refitted the old one back in so it would still be mobile should I had to move it or tow something out the work car park. I popped my meter over the battery just out of curiousity and hey presto, 14v. So it really was just a lack of tension that caused so much grieff! I knew it'd be something silly!