[AT] Tractor wiring

[Greg Hass]

After several years of procrastinating I am going to completely rewire my 
Farmall 856 with a year-a-round cab.  I can rewire a house, a barn or a 
shop.  However, when it comes to tractor wiring I can't figure the size of 
wire to use when it comes to wiring the various components.  For instance, 
I want to add some halogen lights, some hooked together and some wired 
singly.  Also, I want to add a heater and possibly get the circulating fan 
running, which has never worked since I've owned the tractor.

I want to use adequate sized wire, but on the other hand no bigger than 
needed as the heavier wire is harder to work with.  Does anyone know of a 
chart, or source, or rule of thumb on how to figure such things?  For 
instance, with house wiring "amps x volts = watts", but I'm not sure the 
same formula would apply to a 12-volt system.

Greg Hass