C4 Wiring Mystery...

[Craig P.]

I am hoping someone can help me solve a wiring mystery on my 1991 C4...

I recently had my Bose Audio system rebuilt, including the CDM located up under the dashboard on the passenger side. For those of you that have done this, you know it is challenging. It involves disconnecting numerous wiring plugs. I carefully labelled and mapped everything that I disconnected, however when putting it back together I found I had one last plug that had not been labelled... It must have come undone without my knowledge or I would have labeled it and noted where it came from. For the life of me I cannot find where this plugged in. It is a smallish two prong plug with a blue and violet/black wire (picture attached). Not finding where it would go, I reassembled everything, being sure to seat all plugs, and figuring I would find out in short order what was not working, then chase it down from there.

Well, now the speedometer and odometer do not work, as well as the various trip, and MPG statistics. I get an intermitent "SYS" error on the LCD display. Perhaps this is coincidence, but I have to think not. The LCD lighting and all other guages work fine. The blue/violet-black wire and plug is on the drivers side of what was dis/re-assembled under the passenger side dash, and has only 6-8 inches of length - so it can't go too far.

If anyone has some clues for me as to where this connection goes, I would greatly appreciate hearing them!!

[Edward J.]

Re: C4 Wiring Mystery...

Craig, would the be the cruise control switch were it comes out from under column.just a guess.

[Mark E.]

Re: C4 Wiring Mystery...

Is there a circuit with this color code in the wiring schematic? I don't have a C4 so can't help directly.

[Craig P.]

Re: C4 Wiring Mystery...

I looked at what I could find on-line, but did not see anything. Do you know where I can obtain a full wiring diagram??

[Craig P.]

Re: C4 Wiring Mystery...

Thanks much, Dave. Very helpful. I may not be able to check this out until next weekend, but the clues are much appreciated.

I will certainly check out the codes and see what I can learn there. Your instructions help, and I have seen some helpful Youtube videos that show how to pull the codes.

The pic is of the radio CDM under the passenger side dash, correct? Assuming it is, then unfortunately it appears I will need to take it all apart again, but at least I may be able to leave the CDM in place - that was the real bugger to get out... The cruise module did not come out with the CDM when I removed it, but I also did not look for more work to do at the time. It may have been sitting right there, attached with a couple screws... What is the source of the picture? I am relatively new to the Corvette scene, with this C4 being my first. Having some manuals would be helpful, but I don't know what exists, and where I might find them. Any suggestions?

Thanks again! I will reply with what I find...

[Craig P.]

Re: C4 Wiring Mystery...

The Mystery is solved!
So... as suspected, the mystery was for the most part, self-inflicted. As for the mystery two-wire plug, near as I can tell this has never been connected to anything. After spending a couple hours under the dash, there simply is no place this plug can possibly connect to anything, so I have concluded that it must connect to some optional piece of equipment that my car does not have.

With regard to the speedometer et. al., I mistakenly swapped two 10-pin connectors. As careful as I was in marking plugs as I disconnected them, there are two of them together that have an identical connector. If anyone tells you the plugs are unique and can only go together one way, don't believe it.

Long story short, all is working properly!