66-67 Dodge Charger Source Guide

Temperature & Oil Sending Units

Fuel Sending Units (click here)

The sending units for both oil and temperature gauges operate in the same manner. They are nothing more than a heat or pressure related device that screw into the engine block. Heat or pressure causes the sender to vary the resistance in the sending unit and this variance is detected at the gauge by reacting to different readings that it receives. Low resistance results in more current flow between the sender and the gauge, and high resistance results in lowering the current flow between the sender and the gauge.

The gauge is a simple device. The current from the sender passes through a resistor that either wraps around or is located near a bimetallic strip. The bimetallic strip is hooked up to the needle of the gauge through a linkage. The bimetallic strip is a piece of metal made by laminating two different types of metal together. The metals that make up the strip expand and contract when they are heated or cooled. Each type of metal has its own particular rate of expansion. The two metals that make up the strip are chosen so that the rates of expansion and contraction are different. When the strip is heated, one metal expands less than the other, so the strip curves, with the metal that expands more on the outside. This bending action is what moves the needle.

On the Temperature gauge is a white wire that is fed from the Electroluminence Power Pack that creates the wonderful glow for observations at night. Along with the white wire is a Violet blue wire that comes from the temperature sending unit on the engine via the bulkhead connector. There is a brown wire that provides +5 volts that comes from the fuel gauge. The Oil gauge has a white wire that feeds the Electroluminence part of the gauge and that wire is in the same cluster as the rest of the EL gauges.

The Oil gauge has a gray wire that comes from the Oil sending unit on the engine, via the bulkhead connector. There is brown wire that comes from the Temperature gauge to provide the +5 volts to the Oil Pressure Gauge. Both gauges must have +5 volts going to them for them to work, and they must have a good circuit from the sender to the gauge for them to work. Put in simple terms, the bulkhead connectors must be clean and not corroded. Finally, the senders must be good for the gauges to work properly. You can diagnose where the problem is using the following method/methods:

First you can turn on the key, like the car is running and then take the wire coming from the oil or temperature sending unit and see if the gauge reacts or the needle moves on the associated gauge, when you place that wire on ground of the car.
The gauge needle should reflect High oil pressure or High Temperature condition because you have minimum resistance that the gauge is seeing, and should have maximum current flow. If you don't get a needle movement then time to move on. Remember that you must have +5 volts feeding the gauge, so check that point. If you have +5 volts on the gauge, time to move on. Remember that you must have a good current path from the gauge to the sending unit, so time to check the bulkhead connector to see if it is corroded or dirty. You can do this with the help of another person.
Remove the battery cable so that you won't blow up a meter. You do have an ohm meter don't you where you can check for continuity? Get under the dash where the spiders are crawling around and get the wire coming from the sending unit you want to check.
Remove the wire going to the sending unit for the gauge you are checking.
Place one lead of the ohm meter on the wire at the gauge, and the other lead to ground of the car. You should be seeing an infinity reading on the ohm meter.
Now ground the wire that goes to the sending unit, and you should see a dead short reading. You have just checked the ability of the wire to provide a current path from the sender to the gauge in question. You should now know where the trouble is located. <>
Either the gauge is bad, sender is bad, or the current path is bad or the voltage is not there to operate the gauge. If a gauge is diagnosed to be bad, you can double check the gauge by removing the gauge from the dash bezel.
You can use the ohm meter to see if there are any faults in the gauge. You should have infinity between any one post and the case of the gauge. All the posts are there for, is to provide a current path between the sender and +5 volts.
All the gauge is looking for is current, so using a 9 volt battery connect the + side of the battery to one post, and using a jumper go from the other post to the negative side of the battery.
You should see the needle start moving. If it doesn't move, then the gauge is bad. Don't leave the jumper on too long because the gauge is set up to use +5 volts.
While you are in there with the ohm meter, you can test the EL portion of the gauge by checking between the white wire tab and the case of the gauge. You should read infinity.