I have a strange problem with the instrument panel on my 2004 Z06. Specifically, it is the 'MPH' icon. It is normally lit blue as long as you are in the English (not metric mode). What mine does is intermittently go from glowing blue of the normal intensity and then out of nowhere, it will start to glow very dim (at least half as bright as normal). In a 20 minute drive, it will go back and forth between bright and dim a dozen times. While driving, I turned on the parking lights and used the dimmer switch. Everything works normally then. But when driving with the lights off, the problem persists. Battery voltage is good and no IPC codes or check engine light. Everything else related to the I/P works as it should. I must mention this past weekend, I did install a GM power antenna. I tapped into the two recommend circuits that everyone else uses by soldering directly to the two wires necessary behind the fuse block inside the car. I am a master mechanic and realize that anyone can make a weird mistake, but I triple checked everything and it all looks good. There really isn’t much you can do wrong by soldering into the power feed and trigger wires for the power antenna. I used a separate ground wire and the antenna works perfectly. One side note: The antenna goes up as soon as you turn on the radio, but if you turn off the radio (or turn off the key), it takes about two seconds and the antenna goes down. For you guys that have done the power antenna install, is that normal?
Has anyone seen or heard of the 'MPH' icon going from bright to dim?? Help!

 

It's normal. It's tied to the light sensor. If you drive down a tree lined road it will switch from bright to dim as you pass from the light to the shade.