Don't worry about ID'ing the circuit, the point was to make sure that the bulb sockets are clean as well as the bulbs. Corrosion inside the sockets would have been a MAJOR source of resistance, and would have caused numerous problems.

That you got a spark with one of the wires going to the brake light switch is normal, remember this is powered directly from the fuse box through the Hazard Switch. The color of the wires won't really matter since both the inbound and outbound circuits at the switch use a Green/Yellow wire.

The key now is to find out if you're getting a ton of resistance inside the switch.

Once that gets resolved we can begin with further isolation of the problem.

FWIW

E

would spraying battery acid cleaner help on the sockets to get rid of the corrosion?

or should i get some electrical cleaner.

If the switch was malfunctioning would it be capable of causing the problem on its self?