trhamilton,
I'm still a bit confused. The 'R' terminal should not be able to pull the solenoid in as far as I know...only the 'S' terminal. I think your problem is in your keyswitch wiring.
As near as I remember, an aftermarket ignition switch might have a BATT or terminal for power, a ACC terminal that would kill power to the coil but allow accessores to function. The other two terminals would be START and RUN, or IGN 1 and IGN 2.
Your keyswitch should get power from your ammeter - post. If you have a voltmeter, you can confirm that the RUN position is powered when the switch is turned to RUN AND when it is fully turned to START. This is how I think it should work. The START terminal connects to the solenoid 'S' post and pull the solenoid in ONLY when the key is turned to START.
The coil should also be receiving voltage when in the START position, as well as when the key springs back to RUN.
The only thing the terminal marked 'R' should do is pass voltage when the solenoid is pulled in and the starter cranking.
If you are running a external resistor, then the 'R' terminal would be wired to the coil side of the resistor...or to coil + itself.
To my limited knowledge, powering the 'R' terminal will neither pull the solenoid in, or if it is in, it cannot hold it in. It is a simple set of open contacts common with the battery. they close when the solenoid is pulled in, nothing else.
The spring loaded key is the switch that pulls the solenoid in when turned to START, then opens when released to RUN. This is the only way the solenoid should get power.
Does this mini-novel make things more clear.
Stuart