You can get the cooler degree switch for a cosworth from MSD which fits straight into the stat housing on an rst, and the plugs for that era sierra are the same too, i bought a new old stock fan power loom off ebay cause my plug had melted, and it worked perfectly.

But as said the newer stuff should use same plug, i believe the plug on the back of some fans is the same too, i know XR's use same plug, and my GF's mk4 fiesta has same plug on the fan too.

Beware people selling em on ebay for like £40 for the plug claiming they're no longer available, cause theres plenty options left yet!