Hmm. Buzzing isn't good. How loud is it? It's not the "warning" buzz on the back of the unit, is it?
Well, the wiring part is all I could think off. It might be a faulty unit though, but I've never come across one that didn't work (I had 7 in my possession at once, at one time, and they all turned out to be fully functional).
Did you follow my guide on wiring it up, or did you find out yourself? Not to question your capabilities, but I'd like to make sure you did nothing wrong.
EDIT: But you have made sure the ground wires are all good? And how many are there?
EDIT 2: I might have found the yellow wire that you mentioned. Does it come out of one pin, and then back into another on the same plug?
Here's a page from the FSM:
It looks like it's the wire connecting 17 with 21. I've never used it, however. At least, I don't recall ever doing anything with it.
However, if you check the 2 schematics in
this topic, you'll see that the top one connects the pin marked 17 in the FSM page above to both the pin named "Illumination" in the center plug, as well as the one on the plug that comes "out" of the car. Pin 21 is connected to the other pin named Illumination on the center plug, as well as the one on the plug that comes "out" of the car.
When you look at the bottom of the two, you'll see that it's almost the same, however the second Illumination pin on the center plug is mated to the dimmer switch (the one that dims the original cluster, located to the left of the dash, under the left-most vent).
I think 17 might be a ground for the Illumination, just like 12 is for multiple functions. Originally, illumination is controlled by combining the voltages of the 12 to 21 and 17 to 21, where the former has a variable resistor (the dimmer knob on the digital cluster).
Hmm, food for thought. If I ever get the opportunity to install another one of these clusters, I'll surely check!