If you want too try using a typical "changeover" relay (5-pins with a terminal labelled 87a for the normally closed circuit), the pins you would want to use to change the float switch behaviour are as follows:

85(-) .. Energizer coil (ground) ->to the float switch and then to chassis ground
86(+) . Energizer coil (+12V) <-from a nearby KP-II fused power source
87 ..... Load (normally open) -unconnected
87a ... Load (normally closed) <-ungrounded output from the instrument cluster fluid level warning light
30 ..... Load common ->to chassis ground (for the warning light)

Note that in 700/900s the instrument cluster power (typically a blue/red wire on the largest connector) is unfused, so don't be tempted to use that for your 12V source. If you're doing this under the dash, try the cigarette lighter.

For those interested in doing this, the 940 instrument clusters have an unused coolant reservoir level warning light (typically next to the ABS light). 960s had a fluid sensor. There should be an unused 2-pin connector near the reservoir with a violet wire (from the cluster) and black (ground) wire. In 740s, there's a similar unused warning light for the washer bottle level (typically next to the bulb out light). In 700s, and only when present, a 2-pin connector may be found at the washer bottle (typically a black wire plus a red/black wire in 900s or a blue/white wire in 700s), otherwise you have to either try finding these wires at a main connector block under the hood and if not present there then run a wire back up to the open pin on the cluster. The bulbs, when present (with or without the level sensors present), illuminate with all the others when in KP-II without the engine running and when running get their grounds through the fluid level sensors.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now