Sorry, image didn't embed

 

After a bit of reading there are my assumptions

B+ (thick wire), this goes to the starter motor (or battery +?)
Blue wire - goes to the dash for alternator light/exciter circuit
Red wire - should go to dash for tacho, but i don't have a tacho, so its likely going to back of fuse box and hitting a dead end

So, my question is really, how easy would it be to swap the Valeo with a 120amp Bosch....

 

Wit no tacho, should be dead easy.....almost plug'n'play.
Possibly....you may need a longer belt, as the 120 is slightly larger.


Edit:
Just been and looked at my spare 150.
Only has TWO connections....that would be the BIG +ve and the blue wire to the dash exciter light.
Suspect the 120 would be the same.

Mountings tend to be the same distance apart, but as I said, the diameter may be more, so the belt may have to be a few mm longer.