cold at 75F
David85, Thanks for your response-He has 12V at the battery & yes the two heavy guage yellow wires are connected to a momentary ON/OFF switch in the cab on the dashboard. When pressing in the dashboard "switch" 6 volts appear at the wire leading to the Glow Plug relay.
I do not believe cold weather is a problem here in South Florida. "Cold" weather means we wear socks.