electroman29,

Welcome to the Stovebolt. I have enclosed a link to a bunch of wiring diagrams for the '66 rig. take a look and see if this answers some of your questions.

http://rmcavoy.freeshell.org/Truck_gauges.html

This is a free-hosted site so sometimes it won't allow you access until it 'resets'.

EDIT. I looked at the schematics, and they don't seem to show much in the way of specific heater switch wiring.

Stuart