Small burner on replacement Jenn-Air range cartridge doesn't heat

I have an old Jenn-Air electric range (model no. D156B) with down draft, approx. 15 years old. I wanted to acquire a new burner cartridge to replace a old griddle cartridge and add more burners. When I finally found one with the old style 4 prong, 1 round plug connector, I was delighted and ordered two. However, neither of the small elements heat properly (the large element on each works great). Is the problem with the range, the cartridge, or ??? I am hesitant to send the cartridges back to the manufacturer not knowing for sure if they are the problem. I tried them out on the side of the range that had an old ceramic stove top (where the small burner was working fine), and the problem persists.