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!

 

Mine use to do the same thing but at a faster rate. It would flip back and forth about three times in 15 seconds. But as quick as it started it stopped after about three weeks.

 

My present C5 is an '03 Z06 and previously I had a '98 coupe. Both did the exact same thing. Never bothered looking into it. I thought it is weird but it doesn't really bother me since everything else electrical is fine.

 

Thanks for the responses so far. I feel a tiny bit better knowing I am not the only one. I find it hard to believe it had anything to do with me installing the power antenna, but I never noticied it until after I did the install this weekend. Somebody out there has probably had a dealer do a repair to fix this. Can anyone tell me about their power antenna - does it take a second or two to go down after the radio is turned off?

Thanks

 

Update! I figured it out a few weeks ago: It is the I/P responding to changes in interior light via the light sensor that is above the DIC buttons. On a bright day you can cover the sensor with your finger and the 'MPH' light (and the DIC text) will dim.

The system will react differently (more sensitive) if you have tinted windows (especially dark, like me). As soon as you make a turn and chage your relative location to the sun, the system will respond.