My electrical doo dads include a SAE "Battery Tender" cord and a cord for my jacket liner connected directly to the battery. Symtec motorcycle grips from California Sport Touring, presently priced at $36.98 wired to the handy power under the head light plastic.
If I remember correctly the brown wire is positive and the black wire with the white stripe is negative. My hand held GPS uses the same power. The grips heat up nice and hot on high so, the low setting is used most of the time. I have not needed high yet but, I am in the South. So, my heated grips and GPS are on switched power and when I stop the heated jacket liner gets unpluged when I get off the bike and pull the plug... some times in an automatic method.
I added a head light kill switch and use it when I run my jacket liner on high which pulls 76 watts on high so, I didn't want to try it with the head light burning. I use the jacket on a max of medium at night. Its so hot on high I don't even need it unless its 10 degrees or so. I run it on low down to the high 30's, but I do wear a thermal shirt under the jacket when I'm out all day or a regular long sleeve T-shirt on short rides. The thing heats up my arms too much if I wear a short sleeve under it. I wear a Killi 4.0 over the whole get up and I don't quite look like the Michelin man.