Can anyone offer an explanation why a combined rear window and electric mirror heating switch has some complicated-looking electronics in it whereas a simple rear window heating switch (as on the earlier Audi 80) is a purely mechanical switch?
The A6 probably has a timer built into the switch.
Ah, you mean it'll switch off automatically after a certain time to avoid overloading the circuit?
& flatting the battery etc.
More to lengthen the life of the heater elements and avoid excessive battery drain.
OK. I was going to replace the A6 one with an older Audi 80 switch (the pin-out is identical) but this doesn't sound like a good idea now.
Be ok if you remember to turn it off.
I'm surprised the timer is built into the switch. They usually have a relay which makes them quite large.
A resistive heater is a nice easy load to drive, and MOSFETs have gotten really low-resistance recently.
And once you start adding in the mass budget cost of the whole car, wiring to an external relay, ... the integrated solution may be easier.
If it was just me, I would. But the missus tends not to switch it off after use.
It measures 70mm x 20mm x 40mm compared to the mechanical one which is
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