HVAC control head inop on 1998 Buick Riviera

The control head is inop but has power to the head unit. Have replaced two times neither units worked. Between replacing unit every now and then it will have control through to buttons on steering wheel but still none of the lights on the control head work. Please help!

Asked by for the 1998 Buick Riviera
Really need to use a scanner to look at the data stream from you Climate Control head, to see if there are the proper voltages, grounds etc. Or use a wiring diagram to check the wiring going to the Head. That is what I would have to do in the shop.