Need Help! 69 Newport “Brake System Light” always on!

I replaced the entire brake system. New everything. Then out of nowhere my Brake System Light came on. At first it went on and off - from strong to dim. At times it would go off completely. Now it is staying on and it is bright.

Re bled the brakes and they look good. I found that I had a leak at the rear axle brake line and I tightened that up. I thought that was the problem, but the light is still on. Now I found the leak after I bled the brakes. Thinking that I need to bleed them again.

Any thoughts, history, or ideas that I can use?

Is it an electrical problem? Maybe the switch on the proportioning valve?

Any help that could save me some time would be much appreciated.
Author: Maymarmag