Interior Lights flickering again. What do I do?

1997

A couple years a go, my Interior Lights started flashing like mores code.
I had someone check it out. He took the door panels off and did some checking (he had a print out of how to check) with the electrics. He said it was the Body Control Module (BCM) "for sure".

I got a BCM, which did not fix the problem.

I took the dimmer switch out and took it to a electronics repair guy. He hooked it up to a tester. The voltage stayed the same. He slid the slider over and it was smooth. He told me there was noting wrong with it.

I took it to A professor (auto) at the Collage I was attending. It did it all the time except when I drove it there. He kept it all day, when I came to pick it up, he said it never did it all day. No matter what they did, they couldn't get it to do it.

I took it home and never had a problem again.

Fast foreword. I was driving the car tonight and it started flickering again. As I look out the window to the parking lot, I see the whole interior is flashing.

How can I find out what the problem is?

Thank you,
Chris.