Brake Light Live Wire

Long story short my passenger side rear brake light stopped working right before a trip. Lots of swearing and threatening later I have figured out its something to do with the live wire (its not the bulb holder / connector).

Currently I have done the bodge of the week and used scotchloks to splice into the passenger rear brake light and run a wire over which works well enough for the trip.

Is there any point in trying to find the problem with the live wire? if so where would the logical place to start / what would the methodology be?

All the wiring for both sides is behind the internal lamp cover on the offside. Check fuse then for power at the rear under that cover.
I would think that os and ns brake lights as sidelights have separate fuses.

In time scotchloks themselves cause problems with corrosion [ horrible things ] Usual problem is if they have been used to splice in a trailer socket.