It almost makes one wonder if the heater fan system goes back to when cars had a positive earth system
Part of Borghi's dash fix was to reverse the wiring to the fan to the more conventional system so that power goes to the fan from the switch/relay rather than the fan constantly having power and being earthed via the switch/relay. I don't know the technical details of how this was done.
The fan motor itself cannot have a permanent live connection Peter since there are two speeds each requiring a switched positive feed. It's only the relays that have permanent live feeds to their coils allowing ground/return triggers, one each for fast and slow fan selection.
Ground triggered relays tend to be the norm now.
