CEL not working correctly, Instrument panel?

[Themistocles]

My CEL has been acting screwy over the last few months. When I turn the key to “On” with engine off, the light will light up for the test along with the others, But then will stay on along with the battery indicator. Sometimes however, the light will not turn on at all. When I start the engine the light immediately turns off. This situation will continue with or without active error codes in the the system. If I get an error code the light WILL NOT turn on while the engine is running.
What gives? Is the instrument panel at fault? Is it the PCM? If I replace the panel, how would I test a junk yard panel without plugging it into my car first?

[TBLBill]

I'm not sure of the cause, but I know some junkyards will let you bring in a good battery to hook up (if you can find a van with all the electronics still connected) to test it.