Where is the rheostat located?

[slam59]

On my 74 c10 my heater never worked and I never looked into it. But this weekend we were troubleshooting why my headlights would not come on and found out it was my headlight switch had blown and blew out both head lights. Then we saw that the fuse for heater was blown. Put new fuse in and heater came on and all fan speeds worked but would not turn off so we unplugged fan. We did not have time to look further into it and plan on maybe next weekend but friend said that it could be bad rheostat. I looked them up on different sites for pricing but they won't come up. Is this part together with the fan blower or other part and not a stand alone part? Where is it located on the truck?