Jeff,

I'm confused as usual. I would assume because of the weird relationship between dash and engine location that your COE did not come with a traditional tube type temp gauge but did come stock with an electric gauge.

This stock electric gauge has a sending unit in the head somewhere, and when you put your voltage reducer in series with the power wire to the gauge that it no longer reads at all, correct!

You didn't stick the voltage reducer in the line from gauge to sender, right. Wouldn't any GMC item of that vintage be built for a positive ground...I don't understand.

Stuart