High idle circuit on the PT's;

Power comes from the ignition on cb to the high idle switch on the dash (some PT's have a manual valve rather than an Allen Air electric valve) from the switch on the dash to the low pressure (60 psi) switch to the neutral safety switch. From the neutral safety switch to the Allen Air valve (high idle which is normally closed)

When the Allen Air valve opens, it sends air to the transducer located on the left side of the of the engine on the throttle control unit. The high idle circuit interacts with the throttle control valve, making it more or less inactive because of the amount of air being supplied to the throttle transducer. How that works will be explained when I get the write up done on the throttle control circuit. And I find that system interesting.

High idle on the FC's;

High idle on the FC's is controlled by using the cruise control in neutral. Turn the power to the on position. then hit the set switch and each time you do that, the RPM's raise a calculated amount. To lower the amount of RPM's you hit the decel side of the set switch and the RPM's will drop the same calculated amount. To cancel the high idle turn off the cruise control power.