Wow, thanks for the flood of responses guys!

The car is in the garage currently so I presume the mechanic took a look at the fuses (I printed out the relevant sections of the manual for them: fuses, relays etc.), but I'll pick it up shortly and take a look at fuse 35.

@ onehundred80:

I believe the part is unique to the Crossfire but only because of the different icons and colour of the Crossfire button.

I think the only reason for the different part numbers is that the SLK buttons have "ASR OFF" written on them (and are black) rather than the 'skidding car' icon (and silver colour) for the traction control.

Judging from the pictures of the Crossfire hazard switch that you linked (thanks for that!) and the SLK hazard switches linked below it looks like it should be a straight swap, the only difference being the colour and icons of the ASR and lock buttons.

http://www.ebay.com/itm/98-03-Mercedes-Benz-R170-SLK230-SLK320-ASR-lock-hazard-switch-panel-/321232774010?pt=Motors_Car_Truck_Parts_Accessories&hash=item4acaf7237a&vxp=mtr
http://www.ebay.com/itm/2002-Mercedes-Benz-W170-SLK32-SLK-SLK320-AMG-Hazard-Switch-1708202410-OEM-/121259495328?pt=Motors_Car_Truck_Parts_Accessories&hash=item1c3ba10fa0&vxp=mtr
Mercedes part number is 170 820 17 10 which is quite similar to the Crossfire part number 193 820 04 10, though I'm not sure what minor differences there might be between the two. I reckon it's just the colour etc. but again, not 100% sure.

The Crossfire and SLK switches seem to have the same connectors, placement and dimensions. Do you guys think along the same lines, that it looks like they'd be swappable?

I could live with two different coloured buttons for the time being. I think I'll try switching them out myself over the weekend and see if that bears any fruit but I'd like to get your opinions on it before taking my centre console apart!