Wiring for a engine stand
This is what's need to run the car.
The supply can be a junction as shown or joined in any of the connectors if that's more convenient.
This what is needed to start.
When the momentary push button is closed, power needs to go to the starter solenoid terminal and direct to the coil positive.
A 5 pin ECU will get power through the 1/2 ohm resistor.
You can use the starter relay but on a stand I cant think of a reason you ought to.