More likely you have a brake problem. Some things to look at:
1) Is the master cylinder full? Are you loosing fluid somewhere?
2) Have you recently bled your brakes... especially your rears without ensuring the combination valve's (aka proportioning valve's) metering pin was depressed?
Within the combination valve are a couple of pistons... if one or both of the brake subsystems is loosing pressure, you're brake light will be activated by a switch within the combination valve.
Additionally, the FSM says to DEPRESS the metering pin on the combination valve while bleeding the rear brakes to ensure the proportioning valve is "set" between the front and rear brake subsystems. An "unset" proportioning valve will result in the brake light coming on.
Unusual emergency brake occurrence. Recently got the 81 4cyl Scrambler back running but it has a lighting problem. When the emergency brake is applied the lights go out and once released, lights return. As the foot brake is slowly applied I see sparks at the top of the cable guide as the cable is moving. I disconnected the switch and the sparks are still there. I apparently have a "charged" emergency brake. Any ideas where to start?