The wiring on early Alfas is "basic" to say the least. The headlight circuit draws many amps and is run directly through the stalk switch. When you switch a lot of amps you need a good quality switch or a cheap one that can be replaced when the contacts burn out. The Alfa stalk switch is neither good quality nor cheap
To fix the problem it is pretty easy to add a couple of relays to the circuit so the stalk switch only has to switch the small amount of power needed to actuate the relay. That saves the switch and puts the load onto the relay which is generally less compromised than a switch and a lot cheaper anyway.
Here's one I made earlier.