Dome Light - Need measurements to cut hole in room

[Wgesnerjr]

My Custom Deluxe (i.e. Nothing Custom or Deluxe about it) was born sans an interior dome light. LMC was kind enough to carry the housing, lens and wiring; but neglected to give measurement for those of us not lucky enough to choose a Silverado.

So, could anyone give me some measurements on the hole for the dome light? The housing is curved to match the ceiling, but how far up from the back window does it go? Also I'm not sure how to find dead center from side to side.

Here are some pictures

[TKCR]

Are you going to put a headliner in? Because they are meant to be in the headliner, not cut into the roof metal. Or at least, not that I have seen.

[Wgesnerjr]

Yes, plan on a headliner but the back of the housing has an area to snap in the terminals. Once done, these terminals will hit the body if there is not some kind of hole for it to recess into. Can anyone verify?

[Gmc.guy]

Does this help? I'm not sure what year yours is but this one is a 74 might be same on 73-87 but I can't remember. Maybe putting the headliner in and tracing the hole for cut out will work better ?

[Gmc.guy]

Whoops. Upside down. The hole beside tape measure is centre hole for factory headliner trim. Is the light you bought a factory replacement ? Looks different mounting holes

[Gmc.guy]

Find center on the bottom of the window, corner to corner and use a square to find center on the top? Might work

[Wgesnerjr]

Ok, good suggestion. I used the lowest part of the back window pinch weld, (since its got square corners, vs. the top which has rounded corners) measured side to side and got 62 inches, half of which would be 31. So now I've got center of the bottom of the opening. Then used a level to bring the mark up to the top. (luckily, my cab is on a wooden dolly in my garage, so it is level.)

Thank you for the pic, but the screw holes above are for an earlier year. (my buddy had a 78 like that. He had to cut a hole exactly like that.) Has the screw hole for mounting caddy-corner.

Mine is an 85 and the holes are stright across. The Part of the housing that looks like it needs a recess looks to be 2 inches by 1 inch, with the mounting holes stright across. The part is where the terminals snap in from the back side.

I did not grab the headliner board from the junk yard since it was pressed fiber and was disintergrating. However, I just got home and the new plastic board arrived. Yea! Guess what I found? it already has a big hole cut in it for the dome light. Unfortunately, the hole is just slightly smaller thank the dome light housing. So it looks like I will Have to be real precise when I cut the hole.

Thanks for everyone's help but it looks like the new board will dictate the hole.
I appreciate all the help you guys give.

Jay