SERIAL for two Enterprise:
A1 - A1 Reference
B1 - B1 GND
A3 - A4 Status out-Status in
A4 - A3 Status in-Status out
B3 - B4 Data out-Data in
B4 - B3 Data in-Data out

NET for up to 32 Enterprise machines:
B1 on all machines to GND line
A3 and A4 on all machines to STATUS line
B3 and B4 on all machines to DATA line

SERIAL for PC:
A1 reference - GND pin 7 (DB25) / 5 (DB9) Note: this connection shift the Enterprise logical levels to -5V (0) and +7V (1)
A3 Status out - CTS pin 5 (DB25) / 8 (DB9) 1.5K pullup resistor needed to +12V
A4 Status in - DCD, DSR, DTR pins 6, 8, 20 (DB25) / 6, 1, 4 (DB9)
B3 Data out - RxD pin 3 (DB25) / 2 (DB9) 1.5K pullup resistor needed to +12V
B4 Data in - TxD pin 2 (DB25) / 3 (DB9)
The pullup resistors can be connected to DTR pin 20 (DB25) / 4 (DB9) on the PC.

Joystick, simple wiring:
A1 Common pin 8
A4 Right     pin 4
A5 Down     pin 2
A6 Fire       pin 6
B5 Left       pin 3
B6 Up         pin 1

Note: with this simple connections can't used Auto Fire or other electronics in the joysticks. For using these needed some active components (transistors or ICs) for the conversion.

Wow, great work! Thanks!

Now I found one mistake
This book (on PDF page 84) write wrong printer connection 
Now I checked my printer cable, the right connection at EP B2 to pin 11 (Busy) on the printer.
I'm sorry for made some extra work for you!

(???some misunderstand with B1)

B1, Enterprise GND must be NOT connected to the PC. Insted the GND the reference used, with this trick shift the Enterprise logical levels to RS232 levels, from 0V (0) and 12V (1) to -5V and 7V. and the pullup resistors make the 12V from the 7V signals.

pin A4 and 20 must be connected?

The official Enterprise document say A4 connected to both 6,8,20 on DB25.

pin 1 and 4 must be connected?

From the previous document converted the DB25 to DB9, A4 to 6, 1, 4.

I made corrections.
All OK?

Thanks, it is fantastic work!
I think all is ok.

Only the Scart cable need some aditional GND connections.

When I put your graphics to my webpage, what I write for? "Graphics by SlashNet" is ok? Or do you want your real name?

I updated the pictures and make few cosmetic edits.

Thanks!