9 pin connector - dash cluster - 69 'Cuda

First, are the Temp and Fuel gauge working? If not, the Instrument Voltage Regulator (IVR) is likely not working. If the oil Pressure gauge is the only gauge not working, There is a way to test it. One thing I need to point out first. The oil pressure sending unit does not send any signal to the dash. Here is how your instruments work (this might make the wiring diagram make more sense). In you car, the IVR converts 12V to a pulsing 5 volts. It is pulsing because the IVR looks kind of like a set of points that rapidly open and close. The IVR is small and located in the gas gauge. The gas gauge has 3 pegs on the back, and the oil and temp only have two. 12V comes into the IVR in the gas gauge, and then the 5V is fed to one of the pegs on the back of the Oil Pressure gauge. The oil pressure sending unit really should be called a switch, because it doesn't really send anything. Here is what happens (and the gas and temp gauges are the same). The pulsating 5 volt current goes into the back of the oil pressure gauge into one of the two posts, flows through a bi-metal coil strip, out through the other post and through a wire to the oil pressure sending unit. Notice there is only one wire on the top of the oil pressure sending unit. It has a resister in it that controls the amount of current that can flow through the oil pressure sending unit into the grounded engine. If no current flows through to the ground, there is NOT a complete circuit, so no current is actually flowing through the bi-metal strip in the gauge. That will happen when there is no oil pressure. The higher the oil pressure is, the more current the oil pressure sending unit allows to flow through to the ground. This flowing current causes the bi-metal strip to heat up. When it heats up, the coil twists and causes the needle to move. So more oil pressure = more current flowing through the gauge, causing more needle deflection. Here is how the gauge can be tested. The IVR puts out about 5 volts. So take two C cell flashlight batteries in series so as to have 3 volts. Then, using jump wires attached to the two batteries, touch one wire to each post on the back of the gauge. 3 volts should move the gauge's needle to about half way. This makes sense since the entire 5 volts from the IVR would result in maximum deflection. If you have any more questions, feel free to PM me. I can send you a copy of the instrument section of an article on electrical systems that I wrote and was published in Mopar Muscle Magazine about 20 tears ago.