From the Apple //c Technical Reference Manual 

Section 11.2.2 The External Power Connector 
  

The external power supply is attached to the 
internal converter by means of a 7-pin DIN 
connector. The connector pins are identified 
in Figure 11-1 and Table 11-3. 
  

Figure 11-1  External Power Connector 
.     --+ +--       Pin#      Signal 
.   / 7 |_| 1 \     Pin 1     Not Connected 
.  | 6       2 |    Pin 2,3   Signal Ground 
.   \ 5  4  3 /     Pin 4     Shield Ground 
.    \_______/      Pin 5,6   +15 VDC 
.                   Pin 7     Not Connected 

Table 11-3   External Power Connector Signals 

Pin#    Name      Description 
1,7       --      Not Connected 
2,3     Ground    Common Electrical Ground 
4       Chassis   Chassis Ground 
5,6     +15       +15-volt DC input to converter