How can I reset brake warning light?

[72c]

Hi,  Having bought a 1972 Challenger 340 recently, I found that the rear brake fluid tray was empty (cheap line-lock??) and an oil pressure gauge had been installed through the brake light window circle.  I added brake fluid and pumped the brakes until air bubbles quit coming up and the rear brakes began working.  The brake light sensor still indicates a brake warning indicator condition.  How can I reset this?  Thanks

Jeff H.  Challenger Rallye auto

[BIG MIKE]

sometimes you have to bleed the front or  tap on the porporting valve......or both.