Don't hold me to it, but at least on an older Dometic fridge I replaced the Thermocouple on, it connected at the Gas Valve, not at the Control Board. A Flame Sensor, I believe, would connect at the Control Board. The test described above, holding the TC tip in a flame and measuring the millivolt output, would call for a meter. Doesn't have to be expensive. The one pictured here from Harbor Freight is $3.99 on sale, and often free on a coupon with another purchase.
Hardware stores, and probably Lowe's/Home Depot, have generic TC's. So long as you can make the connection and mount the tip into the flame, a generic will work.
