Cab roof question 1991 GMC - Drilling

[RJB44]

I am interested in installing a combination map light and clock unit in the cab of my 1991 GMC Jimmy. I want to put it front center on the inside header area. I have the one piece molded unit with wiring. I want to assume that the sheet metal for the cab roof is two ply, meaning if I drill screw holes from the inside, I won't end up going through a single layer to the outside the of the roof. there are two screws that support this unit. I have puilled back my header material but just want to make sure I am safe to drill in that area. Thanks

RJB44

 

[imiceman44]

I am interested in installing a combination map light and clock unit in the cab of my 1991 GMC Jimmy. I want to put it front center on the inside header area. I have the one piece molded unit with wiring. I want to assume that the sheet metal for the cab roof is two ply, meaning if I drill screw holes from the inside, I won't end up going through a single layer to the outside the of the roof. there are two screws that support this unit. I have puilled back my header material but just want to make sure I am safe to drill in that area. Thanks

RJB44

My 76 cab had 2 layers so i am pretty sure the 91 will too.

 

[BKinzey]

Yep. 2.5 to 3" front & back and about 3/4" in the middle.

Over the windshield there is some bracing as well.

 

[roadnotca]

I am interested in installing a combination map light and clock unit in the cab of my 1991 GMC Jimmy. I want to put it front center on the inside header area. I have the one piece molded unit with wiring. I want to assume that the sheet metal for the cab roof is two ply, meaning if I drill screw holes from the inside, I won't end up going through a single layer to the outside the of the roof. there are two screws that support this unit. I have puilled back my header material but just want to make sure I am safe to drill in that area. Thanks

RJB44

I'm not sure but the LMC catalog may have the parts breakdown.