Some earlier communication and notes exchanged with Alex Herbert and Christopher Tumber.  
This information was also sent to ParaJVE-ParaJVD developer Franck Chevassu (parabellum.fr@gmail.com)

There were two Versions of the VecLink cable were made in the past. Both versions use Vectrex Joystick port two (2) for communications  
Versions:
1 (earlier): Connectors with pull-up resistors and wires. 
2 (later): Connectors with Wires only. 

Test Programs:
Alex Herbert: VL Test, vl_test.bin, VecLink cable version 1
Alex Herbert: Berzerk Arena, BerzerkArena.BIN, VecLink cable version 2

Christopher Tumber: UTG, utg.bin / UTG_2002.bin, VecLink cable version 1
Christopher Tumber: UTG3, UTG3.BIN, VecLink cable version 2

Author ????: DualTV1,DualTV1.bin , VecLink cable version ????
Author ????: DualTV2,DualTV2.bin , VecLink cable version ????


Christopher Tumber:
According To the information I have received from Alex Herbert there are several versions versions of the cable.
Depending on which of Alex's libraries you use the following will be true.
Earlier version of the cable. The I/O on pin 4 is harder to drive than pins 1,2,3 so the pull up resistors were used to try and correct the voltage levels, but even then it was still iffy.
 
The new cable just avoids this by not using pin 4. It means we have 1 less pin for data which should in theory reduce the maximum bandwidth, but I was able to optimise it quite well and didn't loose much performance. 
 
This cable has been performing rock solid.
 
 
Newer style VecLink Cable 
Vectrex A                Vectrex B
1 |--------------------------| 1
2 |--------------------------| 2
3 |--------------------------| 3
8 |--------------------------| 8
All other pins MUST NOT be connected.
(or damage to your Vectrexes is quite probable).

  

Older style VecLink Cable (from picture VecLink3.jpg):
Vectrex A                Vectrex B
1 |--------------------------| 4
      |
      |
      >
     <   600 Ohm Resistor
      >
     <
      |
      |
8 |--------------------------| 8
      |
      |
      >
     <   600 Ohm Resistor
      >
     <
      |
      |
4 |--------------------------| 3
2 |--------------------------| 1
3 |--------------------------| 2