Rusty 54,

Someone on this site probably has the factory sheet that gives 'official' sizes, but a educated guess would be 16 guage wire and a 10 amp fuse.

I have put in a link with some great wire/electrical data. Hope this helps.

There is a online wiring diagram site that shows a schematic for a '54 truck, but no heater info as I think this was a option.

http://www.crowbarelectricalparts.com/Specifications.htm

Stuart