Brake warning light question

Im trying to use as much of the factory wires as possible. I have the msd box, alternator (needs 2 keyed power), Ford Taurus fan keyed power relay, all on the engine bay side. Volt gauge, heater block off solenoid, heater keyed power relay (aftermarket heater) on the inside of the car, gauge lights (plan on using the orange wire from the radio connector so they dim with the headlight switch).

Don't think any of these items will draw a ton of juice.

I am not using the violet temp gauge wire.
I don't have a reverse light although it would be cool to use the oil light for reverse light
Windshield washer motor is available
B and A spots are not being used but have wires on the inside.

On the inside of the car I'm not using the radio.
None of the heater wires
There is a black wire with white tracer that comes out by the ignition switch (looks to be for the reverse gear indicator?)

I have mounted a 4 slot fuse block next to the bulkhead that goes through the firewall. ( on the inside of the car). If I can't find wires to tap into in the factory harness the plan is to use it.