Yes i have the Mackay harness. It did not come with the 240sx TPS. I had to buy and modify one to fit. I did not use the factory fuel pump and efi relay.
I had previously done a l28et swap with stock harness and ecu on my 280z, so the MS3 harness and ecu was basically the same install. See if you can find a l28et swap guide for a 280zx, it might help you to see visually where connections are made.