2001 Marquis spa - underwater light flashing on and off once a second

I have a 2001 Marquis Leisure series spa. The underwater light flashes on and off about every second. It's been doing this for days. Everything else appears to be working normally - it's keeping the right temp, the motor works on fast and slow. The light on/off button doesn't do anything. The all four buttons on the main control need a firm tap to respond. Maybe water has gotten into the light button? I don't see anything in the manual about a flashing light.