You will need to install and Ignition ON/OFF switch for that smaller Red wire on the MSD.
The larger Red and Black wires do connect to full time battery power(red) and battery negative(Black)
So larger red can go to battery post on starter relay(solenoid)
larger black to engine ground
The "I" post on the starter relay can be used IF.........you will be using a ballast resistor between ignition on switch and MSD.
The "I" post only has 12volts(well 10volts, lol) when starter motor is active, it was used to give coil/ignition system a higher voltage when starting a cold engine, so can't be used to keep engine/spark running.
A ballast resistor was used to lower the voltage going to the coil so it would last longer.
With engine running alternator would be at 13.6-14.6volts over time that can cause coil to get too hot and fail(newer coils don't really need that).
The ballast resistor lowered that voltage to 7 to 9 volts which give plenty of spark to keep engine running and coil runs much cooler.
But when starting the engine the starter motor draws alot of battery voltage so system drops down to 9 to 10volts, and ballast resistor would make coil voltage 4 to 6 volts so not great spark especially for cold engine.
The "I" post ran directly to Coil + terminal, so coil got 10volts while engine cranked giving it a "hotter" spark, when engine started, starter relay OFF, "I" post power is cut so ballast resistor power is now being used
You need the ignition ON/OFF switch so battery won't be drained when engine is off, and coil won't over heat from being on all the time.
There may be other systems you want to turn on and off, like gauges and fuel pump?
So setting up a relay bank in the engine bay might be a good idea, the switch on the dash could then just be a ground switch to close relays and activate those systems.
Also to provide power for the "S" switch, so starter can't be accidentally activated
Welcome Visitor! Please take a few seconds and 
