Just purchased a 1999 S320 Petrol. Rear screen heater is not working but heated mirrors are could this be the relay? and if so where is the relay located?

 

Are you 100% sure about this? I thoight I had the same problem and checked the rear contacts with my DVM. Sure enough 13V was present.

I have since learned that the MB rear demister is painfully slow and underpowered. Forget about melting snow.

Might be worth a check before buying an expensive relay.

Best Wisnes,
Ron