I have a dsl40, although I don't know if it is a 40 or 40c by serial number it is a 2013?  I bought this used a couple weeks ago.  It did not come with foot switch.  

I have purchased three of them and they don't work on my amp?  It looks like Marshall has a different pedal for each year.  I have seen pedal numbers (pedl?) 

but those pedals did not have that number on it.  How do you tell.  Sorry for so many questions.  Can pedals on the fx loop and the front input work at the same time? Any help would be greatly appreaciated.

Thanks!