My son's recently put his Mk1 Focus RS back on the road after a 3 year long rebuild.

The Ford ECU is still in place, mainly just to run the dashboard cluster, but all of the engine management is now controlled by an Omex 710

It's running a base map at the moment just so we can get some miles on it before it goes off for final mapping, but we have a small problem with the rad fans.

Both fans start running as soon as the engine starts and don't go off. The water temp warning light is on on the dashboard, I presume because the temp sensor is no longer connected to the Ford ecu (so we need to to sort that), but what's telling the fans to come on? The fans are set in the Omex to come on at 95 and off at 85, so something somewhere else must be telling them to come on.

Could the Ford ECU still be telling the fans to run if it thinks the engine's overheating? Is there another wiring route to the fan motors somewhere?

There's some electronic thing at the top right of the radiator that seems to feed into the rad fan wiring. What's that?

Oh, and the aircon has been removed in case that may have some bearing? we've tried all the usual tricks of setting the aircon switches to certain places etc to no avail

Any thoughts anyone?