[SwissXC90]

Originally Posted by Brianvs60

Sorry to bump this but I'm anxious that anyone with an S60 who can help might see the thread! At this stage I'm looking for help with exploration of the actual tab connection to the heated screen, i.e. with removal of the parcel shelf and/or c-pillar trim.

Any help gratefully received. Thanks all.

Put a Multimeter between a known good ground, and the terminals on the desisted.

On a working demister one side will be 12v and the other side 0v or close to it.

Failure modes:
12v and 0v present but no demistt: suspect broken tracks on window. Repair tracks or replace glass.

12v on both terminals: ground wire broken, or bad ground. Check flex loom, the break is normally in the flex part.

0v on both: 12v wire broken, or fuse blown, or relay not working. Check fuse box, relay, power leaving fuse box. Check for break in flex part of loom.

That covers pretty much everything that can happen.