Emailed schematics to the aol address you have listed for the site.
Basically, the dome light always has 12V on one side. Turning the headlight switch all the way up or having one of the door plunger switches pop out provides ground to the other side. Likely causes are headlight switch turned too far, one or both door switches screwed too far in so they are not pushed in when the door closes, or wire popped off the back of one of the door switches and touching the car body.
Dart 400-AFR 195-224/224 HR-Powerjection III TB with F.A.S.T. Sportsman XFI
TKO 600-Moser 3.42-Detroit Truetrac
'69 Camaro Beater-SFT 327-M20-Moser 4.10-sold
'02 Z/28 vert-stock-sold and totaled
I would check the obvious which is the headlight switch. You know if you turn the headlight switch you can turn the dome light on or dim the dash lights. Then I would check each door switch. The door switches grounds the dome light circut to turn on the dome light.