Ok - so I hooked the first new FCM I bought back up and what happens is the fan comes on fast and then stops, if I cut the grey wire nothing happens, ground the grey wire nothing happens, but every once in a while the fan goes very high for a few seconds and then stops.

I assume this could be both the ECM and FCM? I ordered another FCM - this time a used one as no luck with the two new ones I had.