Stuart,
My 59 is the opposite of what you described for the early trucks. The wiring diagram and harness instructions show the starter wire on the - D side and the other stuff going to the + C side of the gauge. I beleive it was working to the extent that it dropped down when I pulled the headlights on, but I never saw it go past the balance point into charge no matter what I did. If I turned off the headlights the gauge would go back into normal.
If the gauge could not handle the current on the starter wire side - D and it finally failed, it did so in spectacular fashion. If I had high resistance, high heat and it caused the failure, then I have to be able to find out why. Does not seem to me that too many things could cause it since it was a single fairly large wire connected only to the stomp starter top terminal and straight to the back of the ammeter. Terminal on the ammeter was good and supplied with the harness.
If the gauge is a non USA part and I bet it is, and it was a defective part, I am guessing someone else will see the same thing eventually.
As I worked on it today I saw that the stomp end of the wire under the battery cable was not affected in the same way. Looked fine and it was quite clear, as you said, that the grounding took place where it is really fried. It heated the copper up going back to the stomp and melted the tape and insulation, but the disaster end of this business was right at the ammeter. Ralph
