[66_Cat_Jon]

I've recently installed the Master Power disc brake conversion with booster, master cylinder and combination valve on my 66 Catalina that was originally 4 wheel manual drums. The combination valve supplied with the kit includes a pressure differential switch that grounds when there is a loss of pressure and is intended to light the warning light on the dash. This switch only has one wire out of it. The only warning light the car ever had is the parking brake indicator light and as far as I can tell, that circuit only exists under the dash. Is there any wiring in the underhood harnesses that lead to the parking brake light, maybe included for optional power brakes or something? Or do I have to extend this one wire all the way through the firewall and splice into the wire from the parking brake pedal to have a brake warning light?

[OG68]

In 67 the factory connected the grounds from both switches at the firewall plug, and then ran a single wire to the light. If you wanted a clean looking setup you could duplicate that with a spare plug terminal. Or run the differential switch wire through the firewall to the parking brake switch and splice the wires there.

Drawing from a 67 Tempest, didn't have one for the B body.

[OG68]

Originally Posted by OG68

In 67 the factory connected the grounds from both switches at the firewall plug, and then ran a single wire to the light.

I should have said; the factory connected the wires from both switches to the same firewall plug terminal and then ran a single wire to the light.