I'm not really sure what you're asking.

First of all, why did you replace the metal box with a plastic one?

Why (and how) are you adding 12/2 and 14/3? The current wires look long enough.

Wouldn't you hook up your new LED light to the two wires labeled "power to the light"?

Hi, thanks. The electrical is protruding below the drywall and would touch the metal base of the LED light. The current wire length is too short. I used a 3 or 4 port blue to extend the wires. Does it matter which black wire connects to the red wire?

I still have no idea what you've done. Maybe a picture of your current setup would help.

When you say that you replaced the metal box, do you mean the whole huge white box in your picture? Or just the little metal junction box with the cables coming into it?

Are you trying to modify this 1965 light? Or are you totally replacing it?

What is the LED light that you are adding? (Brand, etc)

I am adding additional 12/2 and 14/3 as the existing wires are too short.

First of all, why are there two different size wires? What is the breaker that is protecting this circuit? If there is 14 gauge wire, it should be a 15 amp breaker.

Where are these cables going from and to? All connections must be made in an accessible junction box. I hope you haven't buried a box in the wall or made connections in the wide open.

Does it matter which black wire connects to the red wire?

Red wire from where? Black wires from where?