Early SN diesel 6x4 cut off solenoid burning up

I have an early serial number (in the 3000s) diesel 6x4. The diesel cutoff solenoid keeps getting hot and burning up. I have replaced the K2 relay that runs to the solenoid, the glow plug module, and the ignition switch that was corroded. It cranks and runs fine, but if you turn the key to the ON position without cranking it, the solenoid gets hot and eventually explodes or burns up. I have replaced 3 solenoids now trying to get this fixed.

Any ideas?