The driver side of my (transit tourneo) heated windscreen doesn't work, after checking relays I checked behind the A pillar and found the spade connector had been disconnected and both sides covered in insulation tape, obviously this has been done for a reason, so, me being me thought I'd connect them and see what happens, well after a few seconds the connector gets hot, a lot hot than I'd imagine it should be, so what would be wrong that it makes the connector heat up?

When I say hot I mean I can touch it for a few seconds and that's it

 

The screens are 50/50, therefore only one sides heating elements are working. Due to the draw of the screen a little heat can be expected, but if it's as bad as you say perhaps there is high resistance somewhere in the screen.

Easiest way to test is to connect that side to the working side of the screen.

Martin