I noticed that two of my '72 trucks had a ground strap from the hood to the firewall. My regular driver doesn't have a ground strap.
But it puzzles me that the two hood hinges are steel and make plenty fine OK grounding straps in, and of, themselves.
So why did someone, (I'm not too sure that it was Ford), add an extra ground?
My new radio has some definite crackle but I think that switching to a GM internally regulated Alternator and carbon core spark wires should take care of that.

 

Radio interference is the reason for them. Suppressor or Resister spark plugs also. And also a capacitor at the voltage regulator to handle any alternator noise your radio might be getting.
EDIT. I've also seen these mounted to the coil.

 

Radio noise can be conducted in through ignition. That is why we put condensers on regulators- to filter down the alternator hash. We also put filters on the radio lines from the ignition switch for the same reason.
Hash can also be radiated in through plug wires. That is why we have resistive plug wires. The hash can get off the wires up to the hood which itself is an antenna. It will radiate to you antenna and bring it in.
That is why we ground hoods.

 

Thanks for the help guys. The first stereo that I installed was a 4-track player with AM radio. Kinda dates me that does. But I've been installing audio units for a long time and I've never had a problem with a hood that was steel and had steel hinges. My first Corvette now that was a problem.
I don't think that I've ever seen a Ford Voltage Regulator without a Cap on it. I've run into a few that had bad Caps.
It's just spark interference and I run a solid core coil wire into MSD Heli-Coil wires. This usually works with no interference but I'll swap the solid core for carbon. I have a few leftover ignition filters from previous vehicles that I can install.
Eliminating the noise is trivial.
I just wondered about grounding an already grounded hood.

 

Yes, Corvettes had all kinds of problems because they were made of fiberglass. The cab on our iron acts as a Faraday cage to prevent radiation into the cab.
In desperation, the Corvette guys used to wrap their radios in aluminum foil.
Resistance wires will usually solve the problem.
Hinges- through all the grease and crud- are not proper grounds for the 1 Mhz AM or 80 MHz FM bands. The cruddy hinges act as capacitors and they transfer interference right through. A DC ground may not be an RF ground.
That is why we run solid wire grounds from the hood to the grounded cab. Can't hurt, just do it if you have a problem.

 

"bonding strap"

And you can never have too many grounds (within reason).