Grounding connections '63 Plymouth Fury

I'm hunting down some electrical oddities while looking to install a new radio requiring two hot connections; 1 constant and 2 other is when ignition key is on. The common advice is to check all grounding connections or even add some. As I understand less than 1.0 ohms or 0.5 volts indicates a good ground; lower the better. I added another ground from the neg battery clamp to the fender wall. Where are the motor to chassis connections and any other for the body on this car such as body to frame? The factory manual doesn't indicate locations as far as I can tell. Appreciate any advice.

V8? Driver's side head, negative (ground) battery cable normally goes from battery post to a bolt hole on the head, intake face, up front.
Passenger side head has the same bolt hole, but it's at the rear of the head. Should be a ground 'strap', that goes from there, to the firewall, a few inches under the ballast resistor. That's your engine to chassis ground.

Dash (and instrument panel) should have ground, once bolted into place.

Thanks Miller. I know of the batt neg ground but not seeing any grd on passenger side so could add this. I'm checking the resistance on the batt cable and new grd I added. As for dash the fuel and temp gauges will work sporadically or both will be dead. When I did a continuity check grounding to some areas I would assume are grd and to the metal dash I find continuity; a bright light. I can do further meter checks for resistance and voltage but scratching my head as the gauge issue sounds like a grd problem since both act the same way or could be dash circuitry is shot. Also had wondered about other ground wiring maybe beneath the car frame to body (haven't found any and maybe because there were none).

A problem I had with my 69 Dart, was there was corrosion you couldn't see on the back of the dash studs that the pal nuts screw onto. Cleaned them off, and put regular nuts on them, and my gauges worked fine. I also added a ground to the dash, just to be sure.

Thanks for this info! As I've been reading, ground connections are one thing where "moderation" isn't good unlike eating, drinking, etc.

Just used the battery ground hook-up as reference, so you would have an idea where to look on the other head.
The ground strap used is a flat open braided type, 'bout 1/2" wide...on later models, they changed to a regular cable (I think). Yeah, only those two grounds are used, since the body/frame are unibody...one big ground.

Can only suggest on the dash ground. Mounting bolts on each end...might pull 'em, and clean the bolt threads, and holes. But, only if the ground connection there is bad. And, the mounting bolts for the panel, makes ground for it. Or, toss in a ground wire to the body.
The circuit board on the backside of the panel can go bad, or just need a little cleaning. It can easily be checked using an ohm meter.