On this, take a look here (FABO) for some examples of the '65 wiring.*
Speedometer is mechanical. There should be a cable from the transmission through the firewall to the back of the speedometer.
Alternator. The Alternator gage is actually an ammeter in the battery line. Why Chrysler called it an alternator gage I don't know, but if it indicates discharge, then the battey is discharging and the alternator is not working. When the engine is running it should show charge or be centered (not charging or discharging).
Temperature, and Fuel level are powered through their own instrument voltage regulator (IVR).
Unlike a house or business electrical system, the fuse box is NOT the central point of power distribution.
On a '65 there was a welded splice behind the instrument panel where the alternator output line and the battery line are joined with the power feeds to other stuff. These wires are always hot because they are all connected to the battery positive.
1965 Main wiring
View attachment 1715901140
Turn signal flasher is powered off the accessory splice and not fused.
*examples
65 dart alternator guage
Bulkhead Connector Stripped Threads?
