Hi, having been stranded at a distant airfield, with a dodgy contactor. I can say that the three contactors are not interchangeable, as some require an earth to operate, and others require a positive.
If the alternator is anything like a car alternator, then the initial start field current is supplied from the ignition warning light, just a few milliamps, to get the alternator magnetised.
Last edited by scifi; 31st Aug 2019 at 12:53.