I'm doing a ground up build of a '69 Mustang. The entire car has been apart, repainted, and I'm in the process of re-assembly. I have validated all electrical function including interior lights, dash, etc. I am now installing aftermarket parts (Vintage Air) under the dash that require a good ground and I assumed the dash/frame would be grounded. However, after checking it with my gauge, I found that was not the case. I do have one item mounted the interior side of the firewall and it has a good ground to the firewall. Since I knew the firewall was grounded, I assumed the dash frame would also be grounded since it was bolted to the body.

Should the dash frame be grounded and if so, how is it usually grounded?

 

I know I can use any portion of my dash frame as a ground, and I did:

I drilled a hole, and put in a ground screw.

If the interior was repainted, firewall, then perhaps the paint is causing
a no-ground situation, but you'd think the fastener holes would be
enough to ground the dash frame. Unless, it's supposed to be isolated,
but I doubt it. You can ground it yourself if you need it to be grounded,
just strap-ground it to a good chassis ground at the firewall somewhere.