Basically, I was wondering if there is a different/alternative way to connect or wire the MP3 connector. The bike has about 10 amps total extra capacity. Jacket pulls at most about 7 amps, so running them both should be well within the limits of the bike.
It would help to have a better picture of how all your accessories are currently wired in.
I went to a Fuzeblock so I'd have an easier time. It allows up to 30A draw and hooks right to the battery.
Without knowing what you're using, it's load and where it's hooked in, I'm hard pressed to explain WHY you're even having this problem.
UNLESS you have a problem with your heated gear drawing more than it should and the USB charger just makes it all go over the edge.