Threading headset stem?
 

Had a Raleigh GP shipped to me and am having trouble threading the headset. The big bolt that goes into the top doesn't seem to be catching anything. What am I missing?

Old classic 70's Raleigh GP? They had 1" x 26TPI threading. Most vintage 1980's bikes and Japanese cycles JIS used 1" x 24TPI. So maybe you have different threading? If you're referring to the stem bolt not catching anything, maybe you need to pull it out and look if the wedge is still on the stem or if it's fallen out and down at the bottom of the steerer tube above the fork crown.

What kind of headset are you describing? Look here if not sure.

It sounds as you might have a threadless headset, since you describe a bolt at the top. Of so, it needs either a starnut, or expansion plug in the top of the steerer for the bolt to engage.

Research the correct terminology or post pics.