Major LedfootStarter heat soak - whoa boy; been there done that.
The low coolant level warning light is a great idea. It's standard on the 960s, but not usually hooked up on 940s. Did you use the factory type sensor in the coolant expansion tank? My 945T appears to have the float already in the expansion tank, but the sensor isn't fitted - however I did buy the sensor which is supposed to somehow attach to the underside of the plastic tank. Was this your experience?
Also IIRC the NA and +t 940s used different expansion tanks from factory.
Yup, I purchased an OEM tank from skandix which had the float already in it, and also bought the switch to clip into the underside as well.. From there I grabbed a plug from my pile of spare wiring loom parts to plug into the sensor's (male?) plug and then wired up the rest from there. I remember having to trim the plug because it had a bit of an odd shape, as if it were keyed for the expansion tank plug to differentiate from the other 2-pin plugs all around.
I vaguely remember that not all square-style expansion tanks had the provision for fitting a float switch, but it sounds like yours does have the place for it. It might've been one of those 92+ changes that they made with the switchover from the 740 to 940 era.
Perhaps down the line I'll pull out the cluster, wire in a diode and use the factory position for the coolant level light, but I also like having a really bright LED for 'you should stop the car now' kind of problems.