Thanks. I’m sorry about the picture resolution. I have not found where you can control the upload resolution. They just seem to upload at around 40k. Some advice there would also be appreciated.
The images were of page T5283 and T5292 from the document 1968_GMC_Wiring_Diagrams_After_December_1_1967. After your observation, I did have the wrong circuit for the instrument panel. It should have been T5290, which has the gauge. This was my main mistake.
So it would seem the brown wire from the alternator changes at the bulkhead to brown/white, then splits somewhere to two brown wires, one going to the switch and another to the fuse panel. So my mistake was to think that the brown wire went to the gauge. The gauge is actually wired to the black and black/white wires. So the brown wire, which had not physically been connected to the alternator, is okay to hook up. If my ammeter doesn’t work it’s likely the fuses I the bl &bl/w wires.
Thanks for your help.
I have a new NAPA alternator
https://www.napaonline.com/en/p/RSE2...ywordInput=213 on the 1968 c10.