How many of us are there? Owners of Dodge based RV's?

I'm in need of some help from you owners of the older Dodge RV's.
My problem is:
I have a 77 Dodge RV with 440 engine. I am unable to shut engine off with key switch. It starts fine and runs fine, but cann't shut it down. I have replaced the ignition switch with new one and still have the same problem. Any Ideas. Just about got all my hair pulled out on this, what little I have left anyhow.