TO-35 Key Switch

The key switch on my 1955 TO-35 does not seem to be working properly. The lights turn off, and the engine quits in the last position even after replacing the switch. What could be causing this?

I’d check the wiring to the switch carefully. Keep in mind it is possible you have a bad switch;  It is strange to have two defective switches in a row, but it is possible. Most of the replacement switches available until now are made by WESCO. Steiner Tractor Parts has a new reproduction switch that looks exactly like the original Cole Hersee switch which is still available from AGCO/Massey Ferguson, but is quite pricey.