Toyota FJ40 Fuel Gauge Voltage Regulator Test/Repair

:Gauges - 2nd time's a charm! Getting the Temp & Fuel gauge working again on the 40! And lets not forget that oil pressure gauge.After cleaning the connections on the circuit board on the rear of my gauge panel last week the fuel & temp gauge started working again....for a bit. On the first drive the gauges quit again shortly into the drive...came back on....then quit again. Time to investigate.
After some reading on the forums it looks like the voltage regulator on the back of the fuel gauge is the most likely culprit. The regulator is a bi-metallic unit that opens/closes a set of points to regulate the voltage to 6V for both the fuel & temp gauge. (See video for explanation of it's function). If the regulator fails then both gauges will quit working. I removed the individual gauges from the cluster and tested the output of the voltage regulator (see video), the output was erratic and would stop, start, hang up and then start working again. I cleaned/dressed the points on the regulator and the unit started performing smoothly once again....perfect. Re-assembled everything and drove it around town for half a day....both gauges are working smoothly and consistently. Nice!
More pics and info on my build thread here: www.advrider.com/f/threads/ho...

[@stephenkramme7063]

Mechanical voltage regulator: that is from a different era of engineering. Thank you for the circuit explanation and repair journey.

[@miketrissel5494]

Thanks. If you ever need to calibrate the temperature, the lowest line on the guage = the thermostat opening temperature ... easy as that. If you have a dial type clock there are a set of contacts that close with a clock spring - spiral, and the contacts just need cleaning,
Old timer from when they invented dirt, I should have patented it.