Porsche 1972 911 Workshop Manual page 863

T h e 1975 911 S and Carrera models have a modified relay plate.
1 Relay plate
Standard relay for 1-stage rear window defogger (deleted for 2-stage heater)
2
Standard relay for heater blower
3
4 Standard relay for warm-up regulator
5 Control relay for 2-stage rear window defogger (deleted for 1-stage heater)
-
6 Voltage regulator
Capacitor discharge ignition control unit
8 Radio (interference) suppressor
9 Rear fuse box (fuses S 22 thru S 24 of wiring diagram)
N o t e
T h e relay positions for the heater blower and warm-up regulator were interchanged in some vehicles.