The connector blocks for the cables are readily available as are the pins to make up your own cables there's a few issues
Firstly there's a spacer from the back of the connector block and the cable gland. These were custom made for the Testbook computers including T4 so are not available.
I made some out of alloy tubing and tapped it to accept the connector and cable gland. It needs them both as an adapter fot the connector and cable gland but also gives enough room for the wires to be connected to the plugs.
Getting some suitable 12 core for the main lead can be difficult unless you've got a friendly supplier as it's usually sold by the compete drum
You are correct the Main lead is pin to pin
The various coloured leads are all 4 core which is a little easier to get hold of
the only difference between them is that different pin and bridging of pins with various values of resistor is what identifies the lead when it's plugged into the interface.
I don't have the pin outs and wiring diagrams to hand unfortunately for the various leads at present as the computer hard drive failed, I've got them on back up somewhere will have to see if I can find them.
Russ