AM Radio Light Dims when key goes on?

[motornerd]

Hi All. Any clues on this one? Through trial and error with the radio out, I see that my blue radio light is very bright when the parking lights are on and the key off. But it goes very dim once the key is switched to "On". Any ideas why?

Key Off, Lights On = Radio Light On

Key On, Lights ON = Radio Light very dim

I took the radio out to refurbish it and replace its lamp so I'm doing these test with it unmounted but plugged in. Could that be the problem too, maybe it should be mounted and grounded to work properly?. Incidentally, the dash dimmer is set to the brightest position.

BTW, Testors Florescent Red paint is perfect for repainting the orange radio indicator.

Thanks for your consideration.

[ZmeFly]

is it with the car running and what year is your car.