John Deere 5210 , tractor stalls when key switch returns to run position

[Dave M7040]

I will take your word for it. No reason, I shouldn't. I designed and did (Manual) electronic drafting for production equipment (ARPECO Engineering) for pharma back in the early 80s.

Where is Williamstown?

Just east of Cornwall and near the Quebec border along the St Lawrence River.

Dave M7040