The internal cartridge type are "Polly Heaters", which is a brand name. Polly is reportedly out of business (?) but some NOS does show up on ebay now and then. There were two models, single heat and dual heat. The single heat take about 33 watts and the dual about 33/22 wired in parallel. The 33 watts may dim your headlight when the brake light is activated with a 120 watt system, leastwise it did on my John Deere Liquifire/440 Kawasaki Invader type engine. It was amazing (to me) how much an 1157 tail light bulb draws when the brake light is activated. The easiest fix I found was an LED tail light bulb with brake light. That fixed my dimming problem. Frustrating and dangerous, you have the warmers on, you come hot into a sharp bumpy curve in the trail in the black of night, hit the brake, and headlamp becomes a candle. But then again, I do not know if my sled is producing its rated 120 watts. Its a pull start. Hope my experience is of some help.