Big clue in all those quotes
I bet the 2nd alternator was 2nd hand, not brand new
I bet in both alternators the twin brushes inside black regulator were/are cactus or broken or not touching completely hence noise from motor pully shaft and most times alternator body is very hot to touch and why old battery fubar and the new battery is discharging and the dfi is not receiving any charge hence no spark at plugs.
Battery light on is the alternator/battery charging system
You're right, the 2nd alternator is 2nd hand - I must have bad luck then.
The car isn't starting - I have recharged the battery fully with a charger a couple of times now to be sure - no change.
I can see how what you're saying might make sense with the car running, and how it might apply when the car konked out originally.
But for it not to start on a new, fully charged battery?
Which leads to me to a question I've posed earlier - is the car wired in such an unusual way that it would prevent the car from starting if the alternator broken/brushes in regulator not touching? Because traditionally, my understanding is that the battery starts the car, the alternator just charges the battery.
If what you're saying were the case though, you're suggesting that changing the regulator on the alternator might fix the problem?