Shaun,
Wow!! Cars are so much fun sometimes. I assume everything was ok before you started?
The brake light switch has one hot wire and on not hot wire. It does nothing more than connect the two wires together when it is “actuated”. Push the button in and the brake lights come on. You can also have someone stand behind and just touch the two wires together. You can’t hook them up wrong on the switch.
Did you maybe pop a fuse during the switch out?? Under the dash it is easy to hit that hot-wire on a piece of metal somewhere. If you did a bunch of things could happen. The light switch that turns on the headlights is in the circuit. The turn signal switch is the most likely thing to be harmed. It is fun to replace by the way. I typed some decent instructions in a post not long ago. I will see if I can find it. If it is hurt all sorts of weird things will happen. I replaced mine in 1989, and last year my left side brake lights went out. Yes the turn signal switch was the culprit.
I am assuming that the mini tach hookup should not be involved. Although, did you look for a light source for it? Best to take it off one of the dash lights. Did you have the complete cluster out to do this?
Rob