When it rains or gets wet or damp (humid), the instrument cluster fogs up. Again, FYI, this is a 1987 K100RT. I was told this (the fogging) isn't good, and that I need to buy a little O-ring (gasket) to seal the cluster before I ruin the whole cluster (lots of $$$). Is this true? And if so, how do you get the cluster off? I looked for screws, and didn't see any. I think I might be brave enough to do this myself, if I know for sure what I need to do.
This is pretty normal behavior. The cluster has two teflon (?) air vents on the back that allow moisture to escape. My KRS cluster will occasionally fog up a bit in the winter, but dries right out as soon as the sun hits it.
You may want to replace the o-ring, just in case. To remove the cluster:
Remove the pad with the ignition and auxiliary switches. There are two allen bolts underneath that bolt it onto the triple clamp.
Next, look down at the cluster from above, look down the lower side towards the triple clamp. You will see a 6"-long metal bracket with two bolt heads, in between the cluster and your handlebars. Now, look at the underside of the cluster, next to the triple clamp, and you will see two nuts that are screwed on to the bolts in the metal bracket. If you remove the two nuts (10 mm?) on the bottom, you can grab the bracket from above with pliers and pull it out.
The instrument cluster will now pull off of its mountings toward the front of the bike.
Lastly, you need to remove the wiring harness. It is held on by one small allen nut that goes into the cluster through the middle of the plug block on the end of the harness.
Once the cluster is off, you remove the four allen bolts that hold the mounting bracket on, then remove the 12-or-so screws that hold the back of the case on.
You also have to pull the fuel level and water temperature gauges from the fairing, and paint the illumination bulbs in those housings as well.
Red instrument lights! Much better than the green lights!!!