Brake warning light on

1971 Duster with 1973 up master cyl, booster and disk brake set-up. I've installed a new proportioning valve and bleed the system. Everything sems fine except for the brake warning light that'on. The car is still on jackstand so i'm not able to do a test drive.

Could it be the the way i bleed the brake that cause the problem? If i take out the switch, will i loose brake fluid?

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