Gauges Die w/ Headlights On.

Going to and from Carlisle this weekend, I turned the headlights on while going through the tunnels on the turnpike. The temp gauge and fuel gauge both went off when I turned the headlights on. They came back about a minute after turning the headlights off. I have a 68 Dart. I replaced the headlight switch because my dash lights were not working. I ran a ground to the steering column from the new switch. The dash lights still did not work. Then, I connected a tach to my inst fuse and the dashlights worked temporarily. The dashlights did not come on in the tunnels. That is the first time I noticed them not working. Any thoughts on this problem will be greatly appreciated. Thanks FABO.