I have a series 1 1/2 1968 2+2 in outstanding condition and just fixed 3 simultaneous problems on the electrics and am now driving an almost new feeling car! The symptoms were poor charging (dead battery - nothing new there) the ammeter flying back and forth and the ignition warning light coming on at any revs but strangely going off by switching on the lights. This was caused by a busted 3AW unit and a connection to an ignition relay located just below the horn relay. This ignition relay is not on any circuit diagrams but was probably also doing something to the whole ignition system. The relay was fine but one of the crimp terminals was pushed on to look as if it was connected, when in actual fact it was losely connected by the rubber insulator. So the car was functioning but with an intermittent ignition connection. It was probably always like that!
lastly the clock in the rev counter had stopped about a year ago. Took it to pieces and all it needed was a tiny drop of oil onto the top of the post that holds the contact spring. This released the contact to move freely and bingo a new working clock.
You probably appreciate how these small things make such a difference to the whole experience of classic car motoring and I hope this helps someone else with these mind boggling faults.
XKE Data - IE51285
Graham