Hi Paul!

I think you are talking about a single or multipoint injection mini?
(they have these heaters in the inlet manifold)

From experience I have noticed that a lot of people accidently knock
the cable off the heater when they replace the exhaust manifold and
then don't really notice the difference, I think it is only really
noticeable in very cold climates and only at idle, you may notice that
the idle is a little dodgy with it removed whilst the engine is warming
up, apart from that I don't think it makes any difference to the
overall performance or reliability of the engine.

The previous owner may have disonnected it because it had shorted and
the ecu threw a wobbly, try testing the resistance with a multimeter
and comparing it to the service manual value to see if it is knackered!

miniman