still some light issues

I am having tons of courtesy light issues on my 1999 z71 gmc sierra 5.3l. my interior light on the roof doesnt work at all and the foot light drivers side doesnt work either. when I open the door I get cargo lamp on, on the msg cntr (but its not). when I turn cargo lamp on it doesnt turn on but the passenger foot light is on and the msg cntr says cargo lamp on. If I try to turn on my interior light SAME thing, but no interior light.I think its a ground issue but I dont know where my courtesy light ground is located...or if that is even the issue....
any help would be great!

Do you have a multimeter? Finding electrical problems that are NOT intermittent is about the easiest thing to do with a car, 'sides starting it...

Yep I have a multimeter If you could guide me through the process that would be such a big help...I suck at electrical in vehicles.