Help With wacky dash gauges

I get in the 68 Dart GT this morning when it was still a little dark. All is well until I pull the headlight switch on and the left indicator light comes on (solid not flashing), the temp gauge travels way over to the hot side and beyond; the fuel gauge goes over to the full side and beyond.????

I pull over and turn off headlights and everything goes slowly back to normal. What is? Turn the headlight switch back on and on comes the signal light and gauges head outta sight.

Anyone shed some light on this one.

Thanks