I did some checking a few years back when I wanted to do a grip change when I added my 2 + 2 narrow sweepers. Every chrome aftermarket grip at the dealer was wired externally, but you can still get the stock internally wired heated grips.
I have Demon Heat for internal wiring, with this you can use the grip you want, and very easy to mount. My dealer recomended this instead of HD's, they use to break in 2-3 year. He has changed many HD to DH because of the quality is better.
The stock style rubber grips from the PA catalog state not internally wired but that is a misprint. The stock style rubber grips are internally wired. I installed them on my bike last year.