TTT

Here's where I stand:
I made two circuits, both capable of varying the duty cycle of a 20Hz pulse, from 5 to 90%.
One ran perfectly, varying the duty cycle without changing the frequency. At 7 volts. Once the V came up to 14, a FET got unstable. Radio Shack doesn't carry a higher power option. I can find one, but the average guy doesn't have the same resources as my shop.
The other one could handle 14V no problem. It managed 5 to 25% duty cycle without a problem. Any duty cycle higher than that caused the frequency to drift. At 90% dc, the modulation had gone from 50 to 250Hz.
The e-clutch no like "high frequency".
Keep in mind, both of these circuits were built only with parts that could be easily found and assembled. No digital ICs, PICs or anything of the like. This is all Radio Shack stuff, and as a result, it sucks.

I've found another option, based on a comment by a member regarding a DC motor speed controller. I found a $25 kit that allows you to build your own. It has a transistor and a MOSFET that are kinda odd, but it ships with all of the components needed to work, so no part sourcing required.
It will require 4 components to be subsituted, to change the operating frequency, but they are easy to come by.
I think that this'll work -and best of all, it's designed to be assembled by someone who has no more than basic soldering skills at hand. I've ordered 2.
I'd build a prototype based on it's schematics -but I'm missing one component, so I'll just wait until the kits arrive.

I've managed to switch my TOD display (the interface) along with the movements of a 4 position switch. It was actually easier than I thought that it would be. Getting the display switch to jive with the torque splits will be a little tougher. Again, I'm waiting on those kits to show up to see if I can jam it all together.

To sum up:
If you want 4hi only; you'll cut one wire. Put in a switch, a load, and the PWM generator and you are there.
If you want 2-4 control; you'll cut one wire. Put in a switch, a load, the PWM generator, and a rotary switch, and you are there.
BUT if you want a working display, you ALSO have to tap into 4 additional wires, and work these in to the rotary switch.

I'm making this sound tougher than it is -I apologize. I just need a rainy day and those kits to finalize everything. I still have my "eavesdrop" cable sticking out from under my passenger seat, just waiting to do some good.