This shows converting from the stock pressure switch for the brakelights to a mechanical switch. The pressure switch has the problems of it being prone to failure, not working if the brakes lose pressure and being flaky if the brake pressure is not right. Mine in particular had the problem of coming on randomly when the car was parked, changing the switch didn't solve it so I went with the mechanical switch. The mechanical switch mounts in the pedal arm and is easy to wire into the stock harness.
Supplies:
This shows the stock pressure switch (note I've converted to a '67 Mustang dual-resivour Master Cylinder, however the pressure switch still is the same style)
Just below where the wiring for the switch leaves the wiring harness is a rubber plug covering a hole in the firewall. I cut a slit in the grommet, fed the wires thought the hole and re-installed the grommet around them.
Wiring fed through hole, with extension attached. Normally you would use two male bullet connectors at eh ends of the extension wires to fit into the stock connectors. My stock connections were badly corroded however so I cut them on and used butt connectors.
The switch mounts in place of the rubber bumper on the brake pedal arm. There are two nuts with the switch, one goes on either side of the brake arm to position the switch properly. You want it so that it reliably goes off when you release the brake pedal and comes on with less and 1/2" of pedal travel. Use the two female spade connectors to connect the wires to the switch. Make sure you have enough slack in the wiring to allow for the full travel of the brake pedal.
Another shot of completed conversion.