Hey all, might be a basic question but for a board like the speeduino UA4c utilising an IDC40 connector, what will I end up not wiring in when I go to splice it in to the factory harness? For example a MK2 Miata has a 3plug 68pin connector..I know not all pins are used but there is more than 40. So do I end up connecting multiple wires together etc that are suitable? Trying to wrap my head around it.

Obviously substitute any ECU, I just used speeduino as an example.

 

In general, It all depends on what inputs your specific ECU needs, what outputs you want the ECU to send, and all of the various powers and grounds. It's easier when you have a miata specific guide like the stuff over at https://trubokitty.com/#/ms3xassembly. That's for megasquirt, but I'd imagine a lot of the same stuff would need to be wired up to speeduino.

This diagram from speedyefi shows a barebones setup of the inputs for their UA4c board: https://speedyefi.com/wp-content/upl...dog-wiring.png