68 RS SS with manual drum brakes. All new brake components including rebuilt original master cylinder. I used the original switch on the proportioning block and on the emergency brake, Light stays on. Have real good pedal but it does pull to the left a little when braking hard. The BB with TH-400 does stress the manual drum brakes. Have to plan braking a few second ahead of time but not a big deal. Could the proportioning switch be stuck or gone bad? All I did was clean it up and oil the shaft. Can it be tested without removing? Any ideas to get this brake light to go off?

Does it have a switch above the brake pedal, like a '69 ? This switch turns your rear brake lights on. Or is it your dash light, telling you that there is a problem ?

When I pull the brown wire off the proportioning valve the light goes out. I assume this is an indication of either a bad switch or non-balanced system. This may be why it pulls to the left. When I blead the system I started with the right rear, left rear, right front, and then left front. This was an all new dry system when I started. The pedal feels very solid. I'll go back and bleed the system again. Any tips on getting it right? Another post mentioned something about making sure a device was centered. Not sure what that meant.

if your system is ok and bled. try to apply some fast hard pressure the the brake pedal....vehicle not running ! this may re-center the differential pressure switch.

The valve can be recentered pretty easily. Have a helper push the pedal while watching the light. The key will need to be on so the light lights up. Crack one of the master cylinder lines loose and allow some fluid to escape. This will relieve some pressure on one side of the valve. As the pedal goes down, the light should go out. Have the helper yell as it goes out and immediately close the line. If the first line doesn't work, try the other line. One or the other will do the trick. Don't go too fast or use too much pedal pressure or you may send the valve the other way and turn the light back on.

for the pulling to one side- go do a couple of hard stops in reverse at about 15-20 mph. this will cause the brakes to self adjust. i had to do that on my Nova about every other week when it had the 4 wheel drums.

Thanks for the tips guys. I'll let you know how it goes.