Strange. The pix on top should have a single wire going to it as the coolant temp sensor. The other one looks like a ground on a brake line junction. The wiring diagram does not show that. I think maybe a previous owner did some custom wiring.
Ok. That switch on top was on 77 model engines and was a thermal (coolant temp) switch that controlled the advance on the dual point Marelli distributor. Although you say yours is a '78 model, back then the Alfa factory was infamous for mixing/matching, and running-over parts from year to year models.