Do you understand what dielectric means? It is used to block electric current flow. It has it's place (and an important one!) in electrical connections and electronics. It is used in modern auto electronic connections because you want to block current flow! When you have multiple pins in a connector anything that would allow current to flow between the pins would be a disaster. Same with a lot, and most likely the majority, of eclectic connections, if it is possible for current to flow between two points nothing can be used which would allow current flow, this is extremely important. It could not only cause a failure it could be very dangerous as well.
Now in the case of a single point ground on a car/truck or a battery terminal, why would you want to use a grease that one of it's main purposes is to block current flow? The truth is (if you check the testing of dielectric grease) there is not a great amount of blockage to the current flow in most connections. This is because there is enough metal to metal contact that the dielectric grease is not able to block.
So why use it on a ground (or any single connection for that matter) in an early Ford wiring system? On my cars I am interested in maximum current flow through all the connections and especially the grounds. I do not use dielectric grease on ground connections because I want maximum current flow, not to block current flow, even if it is only a small percentage! It probably doesn't make that much difference really, but to me, why use it.
On the Boeing reference, I worked for Boeing military for 35 years in electrical design, so understand the reference you are making. But this is a Ford car with a single current path that we are wanting to maximize current flow between two surfaces with no worry about current leaks to any other surface near by.
If you like dielectric grease, use it, but understand what it is and what it is for. I much prefer a conducting grease for a ground connection.
Here is the definition of dielectric grease if that is of interest to anyone:
"Dielectric grease is a non-conductive, silicone-based grease that's designed to seal out moisture and prevent corrosion on electrical connectors. It also disrupts the flow of electrical current, which makes it good for lubricating and sealing the rubber parts of electrical connectors. It's commonly used in automotive spark plug wires, recreational and utility vehicles, and electrical systems in aircraft."
"It can withstand high temperatures, making it a good choice for engine compartments and similar locations. Many dielectric greases are rated to work in up to 392° F (200° C) temperatures, and some can operate at up to 500° F (260° C). Though there are other greases that can work at these temperatures, they may not prevent the flow of electrical current like dielectric grease does."
