[Cableguy]

Could be an open or short down in the door jab switch. Little push button down by hinges.

 

[Cableguy]

I have had to replace the switch itself. I had the same trouble. On a 89 half ton which is pretty much the same thing. I had to replace door jam switches and dash switch.

There all really cheap to buy from dealer...

Note:The interior rocker light switch not shown