[dbrownlfk]

I just acquired a 1987 911 Targa and drove it cross country home. It drove amazingly and we had an awesome time. The only nagging issue I had was with the speedometer when the headlights were on. The speedo would work great if I dialed the interior illumination to 0. As I increased the interior illumination brightness the speed reduced inversely proportional until the speed read 0 and the lights were at the brightest.

My gut tells me that something is up with the ground and that the gauge lights are using the speedo signal wire to ground back. I'm new to the 911 world and have been studying up on the Bentley. From what I can tell the gauge lights ground internally to the speedo. Does anyone have any other ideas?