Does your transmission shift out of overdrive correctly? If so I would think it would have to be the wiring to your instrument cluster.
You will have to pull the bezel around the cluster off and remove the instrument cluster (6 screws and 2 wire harnesses on the back). Check the harness and make sure your wire is properly seated inside the connector, it should be the White/light green.
I would then take apart your center console and check if you have continuity from the switch to the wire behind the dash. If not, it has to be grounding out somewhere. If you have had something repaired recently that is the first place I would look, if not I would just start tracing the wire back to the dash and see if it is pinched, or scraped anywhere that is touching metal.
However, if it does have continuity, I would start the car, push the O/D button and then check the fuse. (Keep in mind that your alternator will not be signaled on, so you will be running down your battery the whole time it is running.) If the fuse does not blow, it has to be something on the cluster. I would pull the bulb and see if it is contacting everything correctly, and then trace the path back to the connector and look for any cuts, cracks or scrapes.
If you do find something wrong, I would just look for a used cluster off of eBay or a pick-n-pull.
Hope that helps,
Wednesday, March 11th, 2009 AT 8:12 PM