Hi.
I'm wiring in a polo heater. this has two speeds ( I think).
It has the following terminals.
Black (Earth)
Red
Slow
Fast.
If I conect live to Red,Slow,or Fast the motor operates.
I have a switch from an old ford which switches off, 1 & 2.
I think I need to fit a relay? I understand a basic relay Earth,Live,supply to item and switch input. But how do you supply two or three terminals?

Heater - you southern poof!!!

As I understand "Ford" fans the same supply feeds all connections it's just a resistor in series which limits each feed. Therefore your relay is before the switch as it needs only to switch one supply IYSWIM

you would have to use two relays.
why bother with the slow speed do you think you would use it.