Bil if this is a 6 volt system, its pretty easy. There are two wires on the heater, one of which is short and has a round terminal on it for grounding it to the heater case. The other simply goes to the switch. Then, the other terminal labeled BAT on the switch goes to your power source, usually the Ignition Switch on.
If its converted to 12 volts, there is a stepdown reducer in the mix. Then its wired in this order... Ignition Switch (positive) to the Reducer, Reducer to Switch, Switch to Fan Motor. Again, the negative side is grounded to the case. I spent a lot of time on this article that may help...
http://devestechnet.com/Home/Native12VUpgrade#heatersystem
