I have the dash apart on my 69 right now cleaning and replacing a few things. On the 69 all the switches, lighter, gauges, radio etc. are grounded by thin metal strap’s connecting each to one another and to a grounded source. One source is where the light switch mounts, another is a stud that mounts the bezel to the metal structure of the dash. And where radio shafts mount. Have seen images of the straps on the web and some originals for sale. Have not seen them reproduced. The 69 uses a printed circuit for the instrument cluster, if a 67 uses one the grounding might be the same. I can’t remember from my 67.