They dont come with them.
I got one on Ebay
It was easy to install direct plug in,you just have to cut out a notch to bring the wire to the front where the plug is.
If you noticed the insulation is there for the strip(its like a oven element but shaped like a light bulb.)
It works great when hooked up to electric but you cant adjust temp, its on or off so at night I use the gas heat.
2007 Fun Finder 189fbs Scrapped 4/16
2006 Hummer H3 1983 Honda CX650C
1968 Oldsmobile 442
2017 Keystone Summerland 1750RD