I think I've cracked the problem with my alternator
. Had been driving the car with an alternator off a 1990 1.3 Lancer 
but it was proving too weak (see note 1). It charged to 14v but the battery light was always on, plus, the battery was continually depleting and eventually dying, had to jump start a couple of times 
. I was told the rectifier was probably gone on the Lancer alternator. I think if it were working properly there would've been no problem.
Got a new regulator in the FTO alt and installed it on the weekend and now charging at 13.8 - 14.1v with battery light off. I am still cautious, though, as this normal behavior has happened once or twice before, after installing the alt then about a month later back to 16v and fluctuating.
A couple of things I have noted;
(1) There was a drag off the battery from the internal door lights, cause the contact switch in the door wasn't tight, you'll notice if you close the doors and then push in and out, if there's too much play adjust the door closing (This is why I had to jump start the car a couple of times as the battery was o.k. again after driving for a while,
(2) We checked the earth wires and ran some extra wires directly to the alternator in case it was bad wiring,
(3) The Lancer alternator never overcharged, which I think means there was no shorting occuring outside of the alternator and no shorting in the Lancer alternator. This could mean there is shorting occuring in the FTO alternator. Had a chat with someone in the know and they said that an impact like a bump in the road with hard suspension in the car, could cause the regulator to touch off the body of the alternator and short, which in turns causes a bypass of the regulator, hence erratic charging. If this were the case, then each time I took the alternator in for the repair man to look at it, he took the cover off and probably released any contact which could cause shorting thereby temporarily fixing the problem until the next shock. The test for this theory of course would be to deliberately cause a short on the regulator to examine the effects on the voltmeter.
Hope that is useful to someone, its a lot of trial and error and painful waiting to see whats gonna happen, and the risk of finding yourself on the side of the road needing a jump start
. Still, better than forking out over 1k yoyo's for a new alternator. I'm gonna get a new rectifier in the Lancer Alternator as a back up anyway. If anyone needs to try this route contact me as you will need to get a small bracket fabricated and some longer bolts as the Lancer alternator is a bit smaller. If the Lancer alternator didn't work, I would have tried the Galant alternator (same size, but, 4 pin connector).
DISCLAIMER: Of course I'm not an expert and please note this may have been a specific problem with my car, I couldn't accept responsibility for something going wrong (i.e. lots of blown ECU's), but I think even through researching the UK and Austrailian forums, this is the closest I have got to figuring the alternator problem.
Mitsinut.
. Luckily though, checked the oil pressure, at it seemed o.k., and the next check was on the oil pressure switch. It turned out to be faulty so we got a switch off an old diesel lancer and it worked. Would like to compare the oil pressure readings off something though as I don't have the technical data on the required pressure. Do you know? The readings we got when the car was hot, were;
