Hi Julian
I believe your Fulvia had a change from dynamo to alternator; specifically a Ducellier 7553A?
Presumably it's therefore effectively what we'd see on an S2 with three wires going to voltage regulator; one to starter motor; one to warning lamp. Thus covering your five wires.
In terms of connectors on your alternator then fortunately Colin, in another thread on this forum, took a picture of the 7553A. That is here:
https://www.lancia.myzen.co.uk/forum/index.php?topic=682.msg12423#msg12423The EXC, D+ and D- will tally with the same named terminals on your (presumably Ducellier) voltage regulator. The other D+ is what goes back to the dash warning light and then the B+ (whilst indicating 'battery positive') is what connects to starter motor.
If that doesn't tally then come back!