I think it's part number 76000862; seems reasonably priced, $58. Just not sure how well it works.
Tried hiding the stock one under the fender - reception sucked.

 

I installed one from J&M Adio inside the fairing on a 2006 Ultra. The reception is surprisingly good.

 

It was the very first thing I bought for my 18 FLHX. Within a week, I took it off and threw it in the trash. The reception was horrible. It was so awful I didn't even try to sell it for $20. I wouldn't wish that frustration on a perfect stranger. Instead, I followed this YouTube video. Reception is just fine. The only positive that came from the kit was the plug for the filler panel.

 

I just hid my antenna and probably lost one bar on the reception. It's fine for me because I play Pandora lots.

 

I tried the hidden antenna routine and I lost reception...ended up putting the stock antenna back in the original position. Haven't seen or found anything better than stock yet. Tried a shorty that did not work well either.

 

I use the HD hidden antenna on my 2009 UC's stock audio system. Reception is not too bad... I get most the stations with the hidden as I get with the tour pack antenna.

I have the tour pack detach kit and ride with and without the pack. I installed the hidden antenna on a "Y" adapter on the back of my head unit... the other end goes to the TP antenna (when it's on the bike). I do notice a difference when running only the hidden antenna, but it's not too bad.

I live in NW Georgia... about halfway between Atlanta and Chattanooga. There are not a lot of local FM stations... most are 45+ miles away.

Ride Safely!
John.

 

I took my tp off last winter and installed the J&M hidden antenna in the fairing. Reception sucked a big one.

So this winter I completely swapped out the audio for aftermarket and have installed the antenna that came with the Scosche install kit. Now to be fair I still have feet of snow in the yard so haven't had the bike out for a real world test but I can tell you that in comparison of the two from inside my garage with all the doors closed the Enrock has double the reception of the J&M, but could that also be related to being connected to a different head unit? Don't know.

Just my experience. Reception is all about the antenna and when it comes to antennas, altitude and clearance is everything

 

I bought a cheap $20 one off Ebay.
Actually works really well. Picks up better than my stock antenna.
https://www.ebay.com/itm/Hidden-ANTE...ss!26202!US!-1

 

Where did you get the Y adapter?

 

Amazon...