Decided to post a pic of what I'm talking about.

The top part of the pic shows the inside front of the unit. Inside the red circle is the push button. The red circle in the middle part shows and indentation on the front of the burner unit. Lastly, the bottom part shows the grill unit. As you can see, there is nothing to come in contact with the push button.
I'm thinking that when the grill unit is inserted, the button is not depressed and the fan comes on when you ignite it. When the burner unit is inserted, the front of the burner depresses the button and deactivates the automatic on feature of the fan when igniting.

Now back to my original question, how do I test this?

Just heard from the good folks at Jenn-Air. They are unwilling to provide any technical guidance due to liability issues. They are however, willing to send out a service tech at an exorbadant rate.

I have a Jenn-Air Model JGD8130ADB gas cooktop with both the interchangeable left side sealed burner and grill unit. I know the fan is supposed to come on automatically when grill burner is on, but it also comes on when using the left side burner unit. There is a small push button in the front of the grill/burner housing that appears to line up with a small indentation on the burner unit. I'm guessing this has something to do with it. I've read that the grill unit is supposed to have a prong that pushes a button that activates the fan, but there is no such prong on the grill unit.

Could the switch the problem and is there a way to test it?

Thanks in advance for any assistance.