I had the same problem after doing some detailing on the interior of the car. Indications were exactly the same, moving the headlamp switch past the detente caused the fuel gauge to go to empty and both signal indicators came on. In addition, when I turned the turn signal on, it acted more like a hazard switch than a turn signal. The left and right illuminated alternately. I cleaned all the grounds in the engine bay and made sure I had the tooth washers on both headlight grounds since I had previously had a nose clip restoration. Still had the same indications, only each time I tested the circuit, I received different lighting variations. I went through all of the forum posts on this and knew that I only had a couple more places to check before breaking down and replacing the switch or the entire turn signal wiring harness. I noticed that the center screw that secures the instrument cluster was protruding slightly further than the other two. With the headlamps on and the directional signals activated, I tightened the center screw securely and immediately started noticing the proper operation of the turn signals and the fuel gauge went back to a little less than full which is where it should have been. Since I had cleaned all the grounds and secured with new tooth washers, all of my lights were significantly brighter. Thanks to the forum for all the info on this.