I was in the process of installing a vaccum/boost gauge on the X today, and when connecting the wiring for the light (in the gauge), I came across this dilema:

After removing all of the dash panels, and tracing the wiring from the headlamp switch to the dimmer switch to the instrument cluster I found the wire that controls the variable lighting of the instruments. Great, until I find that the voltage going to the wire is higher when the dash lights are dimmer (reverse of normal operation).

I know wiring, and triple checked what I was seeing (along with pining out the rest of the harness to no avail), and ended up hooking the light up on a non-dimmed circuit.

Here's the question, does anyone know if the X uses a "multiplexing" computer system for running the gauges, etc. I have noticed about 3 boxes under the dash, and though I found the fuse box, there were no relays that I could easily see - which leads me to the aforementioned explaination...

Does anybody have a clue?

Presumably the lights in the dimmer circuit are connected to +12V and then the dimmer rheostat provides the ground path. That would explain the voltage characteristic you saw.

You just need to be sure your gauge light has both wires isolated from ground (the gauge casing) then you can hook it up the same way.

I don't think the X has any multiplexed circuits.

Paul, not the case - when using a DVOM the ground lead (black) was connected to chassis ground, and the positive (red lead) was probing - when the dash lights are dim +12.6V, when they are bright +6.2V. I did have the meter hooked up correctly, and tested EVERY wire at the back of the instrument cluster, light switch on the steering column, and the dimmer switch. They could have changed things since 1999...

You are hooking up the meter incorrectly.
The red lead goes to +12V and the black lead probes. Try it again...that's the same way the dash lights will be hooked up.

I'll try it...

Hey paco, when you are finished how about a post with some pics of the install and what gauge are you using and where are you putting the gauge. I'm interested in doing this too, but I don't really know where to get started?