With access to the resistor, check for voltage from the switch.
If you can, apply 12v to the fan motor and see if it runs then.
Evo was a development of the Grande I think, which has its roots with the Corsa D. Corsa D had lots of problems with heater motors early on, might just need a new one. Ebay will probably supply one at a reasonable cost.
As Nigel says the wiring is GM design..
Not uncommon to be burnt..and a new loom section is half the price via a Vauxhall dealer..(unless PSA have changed pricing)