The Gauge Doc
Checking Gauge Function The three gauges in most 60-74 Mopars use a bimetallic strip wrapped with insulated nichrome wire to provide pointer movement for the fuel, oil pressure and temperature gauges. These gauges work by a points type voltage limiter which takes a 12V DC input and reduces it to approx 5V. On the 66/67 Charger, this limiter is located inside the fuel gauge. Other Mopars have the limiter either inside the fuel or temp gauge, or mounted externally on the printed circuit board on the rear of the cluster. Over time, the points tend to stick, intermittently sending 12V to these three gauges. The insulation on the wire can’t take much of this extra heat generated by too much voltage and over time the insulation begins to char and eventually will cause the wire to burn through and break. Once the insulation begins to burn off, gauges will start to read incorrectly. When the wire burns thru, the gauge will cease to function altogether. To check whether the wire has burned through, use an ohmmeter and measure on the two posts as shown below in the picture (66/67 Charger gauges used in the following pictures)
Note: A 1966 Charger tachometer can be tested by hooking up a 1 1/2 volt D cell battery between the two terminals on the back of the tach. The gauge should read about 2000 RPM plus or minus a few hundred. (585) 615-0456