I have a 1990 corvette 5.7 with 6 speed,car also has c68 option (electronic climate control). it has 102000 miles on it runs great .the problem is with the key on engine off the digital speedo and hvac controls work great ,until you start the car ,then the digital display starts going crazy flickering,the hvac controls go blank and inoperable . there are no codes coming up from the ccm or ecm ,and no history codes . i have since changed out the hvac head unit ,programmer, and instrument cluster,new battery , new cables, cleaned all grounds listed by alldata ,and nothing has changed . also tried wiggle test and cant seem to make it stop.any help would be great. oh yeah the orange colored back lighting of the cluster and hvac work , they aslo dim with the dimmer switch. Response: have you tried wiggling the key in the ignition when not running to see if the same concern happens?