The red "brake" light? It can be a bad accumulator ("bomb"), broken wiring to the hydraulics reservoir cap, same for brake fluid reservoir cap, loose belt on the hydraulic pump (I once found the adjuster screw completely unscrewed. Lucky I didn't lose it), etc.
Most people only check the brake fluid for the brake warning light, but the brake system use hydraulic pressure to assist the brake. So check the hydraulic fluid for the power steering pump, since the pump provide the hydraulic pressure for the brake.