Good morning--new to the board, and would ask to impose on you with a question. Recently purchased an '86 DL and have been slowly working on stuff. Most recent change was to take out the clock and swap it for a tachometer/small clock. This car originally did have the small accessory tachometer (along with voltmeter, bar, and oil temp), but I had no trouble getting the new gauges installed and hooked up, with one exception.

When I switch on the headlamps, the tachometer dies.

What would be the best way to track down what is causing this? I will also note that the small tach originally on the car did NOT use the striped tach wire, but used a heavier gauge solid black wire as the input. I plugged this into the new tach. Again, as long as the light switch is off, the tach works fine.

Thanks for any help you can give,
Terry O.