I have a Fanatec CSR racing wheel with an optional sequential shifter. Since I last used them I lost the stock PS/2 cable and haven't been able to locate it. I bought an off-the-shelf PS/2 cable but found that only the upshifts on the sequential shifter works, not downshifts (up and down need to register).
I had a look inside of the shifter and the circuit is very simple. It has a square ps/2 female as shown on this page. The connections as shown, excuse the artistry
I am very inexperienced in electronics but this is the entirety of this device's circuitry so I would conclude there is no clocking.
Should all work fine by my approximation (and does for upshift). Examination of a female port as in the link shown above details that it connects to one of the NC pins of the mini-DIN format (left black wire in diagram), thus I am coming to the conclusion that the off-the-shelf PS2 replacement cable does not cater a connection for this pin, does that sound rational?
Edit: I have now solved the issue with the shifter in terms of physically managing to make it work. For anyone encountering a similar issue it transpires that if when looking at a diagram like this on a female connector, pins 6 and 5 are downshift and upshift respectively, each having +3.3V when wheel is powered. Grounding either 5 or 6 to pin 4 (ground pin) will cause an upshift/downshift event to register. My purchased cable and a faulty switch were causing the issue for me