70 C-10 Wiring Problem

[My70C10]

The 70 C-10 I've got has a wiring problem(stock wiring). The blinkers all work, brakelights work properly, horn, wipers, etc. When the headlights are turned on, the dashlights go bananas. One time there's no light at all on the speedo and one of the turn signals is lit or both are lit...turn the blinker on and various lights in the dash blink on and off. So before I start the search till I die pd...Is this a common problem with a common fault or will I have to spend weeks/months trying to find the source.

Thanks for any help.