It looks like the PID replaced the sliding switch, and it now controls the temp.. The beauty of the PID is that it learns the capability of the "heater" and holds the temp within a couple of degrees of whatever you set.
I am speaking from some experience, as I have one I bought for one of my espresso machines to control the boiler. They are great, accurate, digital and very efficient. I bought mine on Ebay. Mine converts AC 250V to control DC Thermocouple with a SSR that is DC. They configure them differently, and I assume the the one used on this smoker is AC in and AC out to just make an infinitely controllable switch to replace the slider.
Bill
<i>There is room on earth for all God's creatures....on my plate next to the mashed potatoes.</i>