Your electrician could not have been experienced at working on Alfas.A friend of a friend.?
Have a word with Mike Buckler the 164 register technical expert.
He was Gatwick Alfa and sold out to Rusper i believe,
Now in semi retirement,and on Cloverleaf register.he is a real expert but now a bit reclusive.
give you more detail if you wish by pm.
Maybe the most cost effective way to solve the problem is to find another 24v 3litre being broken without immobiliser and copy the wiring layout .You would have more spares to sell .
There seem plenty for sale.Tifosi has two .but in Glasgow.Borrow or hire a 164 to compare with perhaps .Thats what the Specialists have to do at times.
Another 164 technical expert is Alfisto Steve of the US Bulletin board He has a fleet of 6 164s.
and totally dedicated to keeping the 164 on the road in the States.
The Alfa GB Customer Service are very helpful and would provide wiring diagrams for a project such as yours.
Nornally these are available through main dealer.
Have email addresses of both if you want.
What have Northants Alfa to say on your predicament.?