Chevrolet Repair: Digital Heater/AC Control, chevy silverado, wiring diagrams

Question
I have a 1990 Chevy Silverado, 350 with auto. Trans. The Digital Heater Control Quit working, will not illuminate at all. I replaced all blower relays with new ones and replaced the digital control head with a known, good control head and it wouldnt work or light up either. I cleaned the terminals on the control head and replaced the heater/AC fuse with a new one.Any help would be greatly appreciated.

Answer
HI WILLIAM, HAVE YOU CHECKED FOR POWER ON THE HRNESS PLUG GOING INTO THE CONTROL HEAD THAT YOU HAVE REPLACED ???? I THINK YOU WILL FIND A ORANGE WIRE THAT SHOULD POWER UP THIS UNIT..IAM NOT AT WORK SO I DO NOT HAVE A WIRING CHART TO CK THIS..BUT CK FOR POWER ON ANY WIRES BACK THERE..SHOULD HAVE 12 VOLTS WITH KEY ON..WE HAVE HAD SOME PROBLEMS WITH THE MAIN WIRING HARNESS THAT FEEDS THIS CONTROL HEAD LOOSEN UP AND FALLS OUT OF THE PLUG UNDER THE DASH..CK THIS ABOVE INFO OUT AND GET BACK TO ME WITH WHAT YOU FIND TO THIS POINT. ON FRIDAY IF YOU GET BACK TO ME EARLY IN THE DAY I WILL CK THIS OUT ON MY WIRING DIAGRAMS AND GET BACK TO YOU IF YOU STILL HAVE NO POWER TO THE CONTROL HEAD..BY THE WAY,, THESE DO GO BAD..BUT YOU SAID YOU ARE SURE THE ONE YOU REPLACED IT WITH IS GOOD,,, CORRECT ??? LET ME KNOW,,,TOM..