Check in the fuse box for a timer delay. It is a silver can, about 3/4" around and 1 1/4" long. Looks like the plug-in starter for an old fashioned florescent light fixture. These were used to keep the ignition switch light on for a few seconds after you shut the doors. They might be using one for all your interior lights. If the contacts arc and stick together, the lights won't turn off. Tapping on it might break the contacts loose, or you can just remove it. If you want to replace it, you'll find hundreds of them in the salvage yards. They don't fail very often.
REAL good observation about the lights getting just a little brighter when you turn them on with the headlight switch. That's a trick I use with the brake warning light on the dash. Three different switches can turn that light on. Observations like that make our job a lot easier.
You're correct about it being related to the radio fuse. The memory circuit for the station presets and the clock must be tied into a circuit that is hot all the time. "Interior lights" is the most commonly used circuit.
Caradiodoc
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Friday, December 4th, 2009 AT 3:11 PM