[dsraven]

the ignition switch sends power to the solenoid on the starter which is like an electrically operated switch that engages the starter drive into the flywheel and also sends power to the starter motor simutaneously. if you have the old "step on the starter" pedal style of starter still bolted onto the engine then you have a mechanical linkage that did this when you stepped on the pedal and you will need to swap out to a different style that has the required solenoid. not sure but it may be just a solenoid swap on the existing starter. if you need to swap the starter then maybe look into a 12 volt conversion starter but research it first ecause there are also different flywheels for the 12 volt starters and they have different number of teeth and possibly a different size hole in the middle.
if you have a v8 swap then disregard all the starter talk, you already have the electric solenoid on the starter.
for amperage draw the solenoid on the starter will not draw more than the ign switch from summit but if you need to run other circuits for stuff that may draw more than the switch will handle you can simply use the switch to turn on a relay which is rated for that circuits draw. that is why you see a bank of relays under the hood of newer vehicles, so the dash switches can be smaller and radiate less heat under the plastic dash. the switch in the dash is just turning on a relay so a small signal wire is all that is required from the switch to the relay.