Out of the blue my dash brake light starts coming on everytime I hit the brakes. Is this how it was supposed to work and it just fixed itself, or is this light for "brake"/park only?

I did use the emergency brake yesterday for the first time ever. Perhaps this is related.

I would try disconnecting the combo valve wire near the master cylinder. it is a single tan wire.
If the stays off. The problem is a hydraulic problem, or a bad switch in the valve.

The das brake light is also a warning light...it measures the pressure between the front brake circiut and rear..if one fails the plunger inside moves 1 way or the other making electric contact and the warning light comes on.
A bad switch is basically un heard off , the mechanics inside are far too simple.

I did use the emergency brake yesterday for the first time ever. Perhaps this is related.

Did you check the plunger switch on the e-brake pedal assembly to make sure it's not making intermittent contact? As well as the above suggestions?

My dash light is on permanently too. I detached the tan wire from the master cylinder and now it goes off/on when I use the parking brake. I had my brakes looked at by a repair shop and they said that nothing appeared to be wrong so I haven't investigated any further.

The most common cause of that dash light coming on when you use the brakes is a leak. In fact that is what it's there to warn you about. Check the level in the master, I'll bet one side is low.

Also note brake fluid doesn't just get low. It can only leak out. A leak in the brake system is serious and dangerous and must be located and fixed pronto.

Just to get things right..is it on all the time or just when u press on the pedal...hard?
If its on all the time its not a hydrolic fault but a bad ground or short somewhere.

Just when I hit the brake pedal.

So this light only comes on when brakes are malfunctioning?

As suggested, if light comes on when stepping on brake pedal, there is a problem, hydraulic side, usually a leak, or brake shoes worn or brakes needing an adjustment.

Check the backing plates of all wheels or the inside sidewalls for leaks showing as wet fluid and thr reservior for low fluid. Both halves of the reservior should be the same level if no leaks. If one reservior is lower than the other, the lowest side is leaking; front reservior, front wheels, rear reservior, rear wheels.

If you find no leaks, then the cause may be worn brake shoes and in need of replacement followed by adjustment of the parking brake and added fluid to level off the reservior.

Or a simple adjustment of the brake shoes against the drums. If brakes are out of adjustment, it will take more pedal to move the more fluid to fill the cylinders to press against the drums. If the light comes on and goes out upon release of the pedal, then I would suspect the shoes needing adjustment, if not replacement of the brake shoes. Sometimes, the self-adjusters get stuck and don't adjust due to rust and/or not being used.

Sometimes, the self-adjusters get stuck and don't adjust due to rust and/or not being used
Covered in the owner handbook..should read it guys.
The adjusters work when u back up a stop with the brakes on..hence, from memory they mention it is not good practice to stop in reverse with the transmission.
Well the theory is right, in practice the drums get full of crap, moisture and stuff, then about when the brakes are are about 2/3rds worn the adjusters stop working.
Always back off the hand brake before adjusting rear brakes, then adjust up the hand brake

I had this porblem on my 68. There was a vacumm can on the firewall behind the drivers side fender. The hose has rotted off. I replaced the hose and no more problems. Manual brakes, not sure what the can actuallu is for.

Rear cylinder was very low. filled it but problem light still on. I noticed brake fluid around the outside of the passenger rear drum brake.

Leaky rear wheel cylinder. Change it out along with the other side, new shoes, new springs. Check the drums? Should be relatively flat and round, no oval shape.

Use BraKleen® to clean out the brake fluid in the pores so new shoes will not get contaminated. How about the rear hose from the body to the axle? Has cracks? Might as well replace it while you're there.

Front hoses, cracked? Change them also.

Now to reset the block, pump up the brakes as in bleeding and hold the pedal, open the front bleeder and the block should reset to center itself. It might need a little pull to center. You have to reset the block as bleeding the rear brakes will not happen as it is blocking off the rear brakes, big hole - nifty device, huh?

Thank you very much. Can I get this old 1968 wheel/drum cylinder from Auto zone/summit or do I have to go DRclassic to find this stuff?

Thank you very much. Can I get this old 1968 wheel/drum cylinder from Auto zone/summit or do I have to go DRclassic to find this stuff?

If you are not worried about numbers/parts/whatever matching ... You can try a local NAPA or whatever parts place. I'm thinking they might have it or be able to get a replacement for you.

If you are not worried about numbers/parts/whatever matching
Or have a dig around a couple wrecking yards...

Parts stores have them. $9.99 at AutoZone. Novas and the like are the same.
Part #: 33447
They've got all the replacement parts for rear drums.