1969 Dodge Dart Custom Sedan Slant Six, Father-Son Project

Thanks to this forum, the Instrumental panel Voltage Regulator (IVR) was the likely culprit. Wow, those are expensive, and what a weird design in the first place! Apparently it provides a 5V RMS to the fuel and coolant temp gauge, with a capacitor thrown into the circuit for good measure. Good luck testing the old IVR output with a digital voltmeter (signal bounces too much to be read).

Our cheaper way of fixing this required a little bit of extra time, compared to just swapping out the IVR with a new one.

At the auto parts store we bought a $12 generic USB charging port. It puts out a steady 5.1 volts DC given an input voltage of 9 to 16 volts DC. We had an old USB charging cable laying around that we repurposed. Grab a solder iron, crimp and solder on some male spade connectors, and there you have it: 12VDC input to 5VDC output, which plug right into the back of the instrument panel.

We did need to feed it a switched power source, so there is some additional wiring work needed to feed it. In our case, it came from a new fuse panel that we added above the existing fuse panel (provisions for future circuits).

Plugged it in, and...... still no gauges! :???: