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.
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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.
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You can use the starter relay but on a stand I cant think of a reason you ought to.