The heating pads are physically sewn to the leather. Do a search on heated seats and you should find pictures by me on how to sew them in. As for whether the 300SEL has the relays or the wiring for them I don't know.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.