Your bike probably has (or had) a battery sensor of some sort.
When the sensor isn't used, the warning light flashes. I don't know the simplest way to disable it.
The 82 750-R1 battery sensor has a pink wire that needs to be connected to a switched 12 VDC source.
The brown wire circuit would be one way to do it; the horn is usually on that circuit.
The brown wiring coming from the ignition switch has a bullet connector, so maybe a double connector could be used there to attach the pink wire.
1981 KZ650-CSR. Competition, Sports & Road.