There is a possibility of a bad ground, but this looks more like a main power feed to me.
Fuses to check:
#11 and #17 in the main drop-down panel on the driver'* side. These power the Hvac Programmer. #17 also feeds the ECC control head.
Next question is do you have the stock stereo or aftermarket? The stock stereo in 92/93 cars with ECC controls the display brightness control for the ECC display. Do your buttons light up, and just the display is out? Or the display and the button backlighting? They come from different sources. Button backlighting comes from the headlamp switch/module. VF display brightness control on the ECC comes from the radio.
With the instrument panel lights on (headlights on), and set to bright, what do you read on the purple/white wire on the back of the ECC? It should be Pin 2.