[banditcilik]

thanks for the responses. since this is a relatively low powered vest i was hoping you all had a trick to run it off the dashboard power. i'll abandon this project and just use the battery for now and get a more powerful vest next winter!

I have the same kind of vest made in China, bought it for about $24 if I am not mistaken. I just wish I bought a size smaller.
I use the cheap USB charger with 2 amps capacity and wire it to the bike battery. Don't use that fancy QC thingy, they are meant for charging cellphone. They have Qualcomm chip inside that needs to communicate with the load before pumping high amps.