Heated Rear Window

I have a '92 500sl with an annoying problem. The heated rear window in the hard-top doesn't work. Obviously I've checked that it's plugged in, and the dash warning light on the switch comes on but it just doesn't demist. Anyone have any thoughts?
Many thanks....Kenny

[Gilly]

I'd get a voltmeter and see if you have a good power supply and ground at the body side of the connector for the defroster.

Gilly

[kip Foss]

With the volt meter check the continunity of the window heating wires. I think that they must run in parallel so one broken wire should not runi the entire system. Ask the dealer how the system is wired.