ok, i've seen a lot of threads about how vacuum lines, blend doors, etc are problems that need addressing on the electronic automatic temp controls (eatc). mine does not have those issues. mine seems to be power to the control unit itself. where exactly does its power come from. my unit has digital readout of outside temp, inside temp, various functions etc. when there is no power to the control, or it doesn't light up, the fan blows on high and the is no control. but, and this is a big but, every now and then it just works! it lights up, the controls operate fine, then out of the blue it quits. now is it powered up by the fan motor resister unit, which i have found. it has 2 wires for the fan motor and 3 more wires for whatever. i have pored over wiring schematics and searched throughout the truck and have found no wiring or fuse or relay issues. i'm just not going to buy new resister or head unit just to find out it was not the problem and i'm back at square one. does the control unit get its power from the resister? and why would it be intermittent? i thought if electronic failed, they failed, not work now and then.

PUZZELED IN ARKANSAS
2003 F-150 Lariat extended cab