When I turn headlights on, all guages go to zero, and stay until lights are switched off. Any thoughts are greatly appreciated. I recently purchased this car, and I'm already a few thousand into the rebuild process.

'81 Vette

I'm not in electrical.  But I would check the grounds and the fuses first.  Then check the console board if that went bad.  Or could be a wire shorting out. 

Some one else will point you in the correct way.  That's just a start.

Good luck in the problem.

I just had this same problem and I hope your problem is as simple as mine to fix.  The plug in the back of the center console gauge cluster worked its way loose or is not getting a good ground as Mike mentioned.  Pull out the passenger seat and the console cover off.  Using a flashlight, look up behind that console and at the plug.  To get my hand on it,  I had to take out my glove box.  Good Luck!

--Eric

The light are supplying the ground for the gauges.  When you turn on the lights, you lose the ground.  The problem is a faulty ground circuit from the lights and gauges.

You can confirm the bad ground by starting the car, and watch the gauges.  Turn the dash light brighter and dimmer, and you can watch the gauges go up and down.

Fix the ground, sometimes easier said than done, and all will be good.