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I noticed the other day that when I open the door the light under the dash comes on but the overhead lights do not come on. Then yesterday when I was driving it I hit the horn and all I got was a buzzing sound from above my feet -- and all three of the interior lights glowed dimly.

Any ideas? Where should I start?

I had this problem a few weeks ago I went through the fuses, and found that the horn fuse was out. It was realy strange, my horn made a bad sound and when I turned up the radio, the light under the dash would go out. I replaced the fuse, and everything works.

I noticed the other day that when I open the door the light under the dash comes on but the overhead lights do not come on. Then yesterday when I was driving it I hit the horn and all I got was a buzzing sound from above my feet -- and all three of the interior lights glowed dimly.

Any ideas? Where should I start?

i have the exact same problem. it seems if i hold my horn button down my interior lights will slowly start illuminating (lights and interiors in a off position). only the light under the dash works properly eg. when i twist my headlight switch, but the interiors overhead dont. i held the horn button down, for about 2 seconds before i became worried i was causing more harm than good. and slowly but surely all my interiors start lighting up! anyone have a explanation for this?
91 k5 scotts

Just like the horn, the interior lights are ground switched. They have constant power, but the switches and horn button apply ground. If this is happening, you should keep in mind that the foot well light draws it's power from a different point. So your footwell light will work, but the dome lights will not, so most likely the fuse is blown.

There was a flasher (I think that's what it's called - little circular thing with 3 prongs on it) under my dash that made buzzing noises when I pushed the horn, and the lights dimmed like that. I found the flasher that was clicking, and replaced it.