You might need to check the connection between the wire out of the exhaust manafold probe and longer wire going to the gauge. About once every 6 months or so I need to mess with this connection. Everything works fine afterwards, it's tight on my truck, but sometimes I can just jiggle the wires and the gauge goes to working.
I realize I need to solder this connection, but haven't found my "round toit".
RJR