Hondata

hello i drive a 00 em1. i have a brand new v4 kpro. the engine shut off while it was running at idle. wouldnt activate main relay afterwards. my friends kpro started my car right up and activated main relay. if i i ground the black wire on main relay, only then can i start the car with my ecu. what can i check in ecu board to see if it burnt out. please help this is my daily driver. ecu was purchased from Full Throttle in queens less than 3 months ago. less than an hour of running time on ecu.

The main relay output transistor in the ECU has burnt out. It does this because too much current is being drawn on the ECU main relay output. There is a chance that the damage occurred before you got the ECU, but unlikely.
The most common fault is that people wire the ECU 'main relay' to the vehicle main relay output, rather than the relay coil side, which will burn out the transistor very quickly.
Check you vehicle wiring. I would not use you friend's ECU as you may damage it too.
Once you've fixed the wiring you can either swap the KPro into a different ECU or change the wiring so that the main relay is energized from the ignition switch rather than the ECU.

the problem occurred when I jumped the fan switch on my conversion harness . I was troubleshooting my cooling fan. As soon as I jumped it. Car shut off. So I know that's the cause. And that the vehicle wiring is good.

Well, at least you know the cause. I'd check the master ground on the manifold (or valve cover) is good.
So the options are to swap the KPro over or re-wire the main relay.

You have any diagram I can follow to rewire main relay. Or if I ground off the black wire on main relay. It's 85 on relay I'll be fine if I ground it too chassis. When I do that it works fine back to normal like nothing happened