Door jamb light flashing intermittently

Hello fellow Celica enthusiasts! Just got another Celica... a 2000 GTS, I've been reading up on the CEL being a problem for some, because of modification . I'm checking into that to see if anything was not done correctly . But, I'm having issues with the door light flashing on and off while driving.. I've made sure all doors are shut, and also manually checked the switches. When the light is stuck on, there's no way to remedy this... Any ideas? Is this something common?