When the surface of copper turns that greenish oxidized color, does the resistance to current flow increase or isn't affected?
For instance if the point of contact is secure and clean but bare visible copper wire has oxidized will it still conduct electricity no problem?
Like this ground wire in my car. The resistance to negative of the battery reads 0 \$ \Omega \$ as well as from both ends of the cable itself.
The oxides are non-conductive as they have a full valence bands, but if you "dig into" the wire, you'll get to metal that isn't covered with an oxide. CuO is pink, but does not complete the valence rings, so you get Cu2O after a time, which is black. The green is either from a sulfate or carbonate. You have CO floating near the engine, you'll have some green after the Cu2O reduces. If you see green near the battery, it's because the sulfur from the the battery has electromigrated up to the connector and gone it a lower energy state there. You see this when you have a "bad cell". I'm pretty sure it's Cu4SO4 with some (OH) hydrated state.
Anyway, you need to take some steelwool and clean off wires in order to remove the oxide if you want to remount them. You could put them in a glass of Coke and have the phosphate reduce the copper oxides. Everything just wants to be at a lower energy level, and if you are there, you don't conduct.
In your photo the corrosion on the outside does not really matter, and it tends to be self-limiting- once a layer forms the corrosion slows greatly.
What matters is the connection between the plated copper or brass lug and the copper wire, and that is a crimp connection. A proper crimp joint is gas-tight and will not allow corrosion to occur within the joint.
To get a reliable gas-tight crimp proper tools should be used in accordance with the manufacturer's directions. A cheap crimp tool that just mashes the lug barrel against the wire is a recipe for unreliability. Good ones are made with precision, hardened dies and ratchet so that once a crimp is started it must be completed before the tool opens.
Here is a photo (from here) of some properly crimped connectors that have been sectioned to show the wire-lug interface. As you can see it's become pretty much a solid mass:
If you sliced open your automotive lug you would likely see a similar wire-lug interface that is a solid mass.
When cars and trucks burn fuel they emit sulfur dioxide and other pollutants (all bad for your health). The sulfur dioxide mixes with the moisture in the air to make a very mild sulfuric acid. this mild acid reacts with the exposed copper and turns it green. This green oxide is non conductive. However the copper wire that is crimped by the terminal connection or covered by insulation are protected from this mild acid mixture and thus stays copper bright and totally conductive. I have seen gold, silver and iron turn black. Aluminum turns powdery white from this same mild acid. You could use a white light grease to seal the metal contacts from the environment and oxidation. We use to use that grease in factory environments where petroleum lubricants (high in sulfur) where used.
Metallic materials, in certain conditions, can develop a thin film of ceramic material for various reasons (it is usually an oxide of the underlying metal). Ceramic materials do not conduct electricity, but the surface thin film is usually confined to a few atomic layers, so it will not affect significantly the properties of the bulk metal (provided the thickness of the metal is not subnanometric).
The surface oxidation does NOT affect the conductivity of the wire unless the degradation is MUCH deeper. You have proved that for yourself with your zero-ohm measurement.
