You need to upgrade to a 100 amp Alt the current alt you have may stall the motor when the fan starts up with the headlights on. You don't need starter relay they are not made to work that way. Ford never use that kind of relay or 6 gage on fans wire its just not necessary.
You can go over to
http://www.thehollisterroadcompany.c...VIIIrelay.html and read up on it and here to see a MarkVII in a C10.
http://www.thehollisterroadcompany.com/MarkVIII.html
you can read here also
http://www.carcraft.com/techarticles.../photo_03.html