M38Cdn Refurbishment

[rob love]

You are lucky they work. I found that usually on those gages, the fuel in particular, as well as the temp and oil pressure, would burn out without a ground.
The later M-series added a short ground wire from the panels to the dash which helped prevent this. There are times that you have the dash backed out (cable or gage replacement) that turning on the ignition switch can have bad results.

Same goes for testing gages on the bench. You must provide a ground to the case or the negative stud before applying power and sending variable negative thru the wire.