Dome Light flicker on both Vans 98, 2000

I've had an irritating dome light flickering on and off on the 98 Astro for years now and have never been able to find the cause. I just bought a nice, like new 2000 and When I was driving it home I found that it does the same thing. I think it is worse going up hills. There is a relay clicking under the dash on the 98 when this happens but not sure I've heard that on the 2000. What could this be?

Most likely one of the door jamb switches is out of adjustemnt. The slider door switch should have a white plastic cap on it, I've seen many that the cap has fallen off. The slider door switch is in the "B" pillar.

Old Master . . . you've got all the good answers.

How is the Great White North?
I don't like to work in the cold either.