I believe that Gerbing was making the internals for HD. I don't know if they are still doing it. Gerbing switched form a round wire to a flat tape wire for heating about a year ago and a factory rep at a demo made a general comment about Gerbing dropping from supplying a large customer. Was this HD? I don't know.
My wife has lots of problems with cold, so I researched this topic and we bought Gerbing liner pants, jacket and gloves for her. Gerbing is simple to use, made well.
If it is not labeled as such, check to feel the heating wires in the jacket. If they are flat, I would say it is Gerbing. Round, could be a old Gerbing or another brand. I would only purchase Gerbing given the quality and their guarantee.
I don't know what kind of jacket you are talking about but most are made to be worn under another protective jacket/leathers. If you haven't you may want to check the fit wearing everything so you don't feel too restricted if your outer jacket is a snug fit. Also know that if you have a favorite jacket, you can send it to Gerbing and they will add a heating system to it.
If it is a Gerbing, I can tell you that riding in 7 degrees F at 75 mph, you can make it so warm that you literally can't stand it. The heated gloves very impressive.