Intermittent light in Radio

If it is a stock Toyota radio/stereo it may have an internal problem in the radio but it may have a bad electrical connection or connection that is not fully seated in its connector. This may be particularly possible if any other work had been done in the past being the dash like heater core replacement or air conditioning work. I have seen the stock stereo fail which would leave you with the option of replacing the stereo or there are several companies that specialize in repairing OEM stereos.