First, Bret, looks as if you also have a 1996 GM. I just pulled out the lamps from my armrest switch panel. Two sizes; one blue base and a smaller one gray base. Each with a blue rubber-y, "boot," over the glass for that color. Base of the larger is 3/8" across. Base of the smaller, gray, one is 5/16th. inch across. Both open, so they're bad; I'll bet they are original to the truck. Bad thing is I'm sure these are soldered or crimped in. I get no movement at all trying to get them out of the base. I need to see if I've got an old headlight switch and find out if it is different, as you said that's what you were working on and the lamp was, "replaceable." I'm studying the link/source you so kindly posted, but am yet to be convinced they are compatible. Not only does the base have to twist and fit, it also has to have the right little contacts to engage the circuit board. Sigh. Everything's a challenge. But when something like these little frustrations are solved, and posted on these forums, it is a Blessing!
B