9 pin connector - dash cluster - 69 'Cuda

Is there a better image / wire diagram that you can point me to?
I have this from the PDF of the 69 Plymouth Service Manual.
I'm troubleshooting an oil pressure gauge - no deflection issue.
I've confirmed that the pressure sensor seems to be good and is sending the appropriate voltage to the dash.
Now the dash is out and I'm................ digging in.

Thank you

cgfen said:

I've confirmed that the pressure sensor seems to be good and is sending the appropriate voltage to the dash.

Click to expand...

I may be mistaken but the oil pressure sender should be a variable resister to ground. It should not be providing any voltage to the gauge.

Classiccarwiring.com has some nice laminated colored diagrams.

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.

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If you have the panel out, a ohms meter on the 2 oil gauge posts should show approx 20 ohms. Open or no path from either pin to the gauge can.
The connector at the oil sender is supposed to have a plastic insulator on it. It is often broken and MIA. If that bare terminal gets knocked off the sender and touches ground, the zero resistance path overheats the gauge until it fails. If the resistor wire is fried it usually shorts to the beam. Contact posts will be shorted to the gauge can. You might see small particles of cooked insulation like black pepper falling out of the gauge.
There is a aftermarket source for that connector with plastic insulator. I didn't save the link to it but it is in other threads here.
For the oil gauge sender, with the engine running, not know what oil pressure you have, resistance from senders terminal to battery neg' should be somewhere between 70 ohms and 15 ohms.

You don't really need a diagram, you can simply look at the cluster and follow the wiring layout

In addition to the above posts, the sender wire goes directly from the oil sender THROUGH THE BULKHEAD CONNECTOR and to the cluster PC board connector ANY point along the way can fail

Make sure you have the correct oil sender. CHECK it for resistance, engine stopped and running

The sender wire path is SENDER CONNECTOR-----------through the BULKHEAD CONNECTOR----through the CLUSTER PCBOARD CONNECTOR----------to the PC BOARD PIN----to the printed trace ----to the GAUGE STUD-------through the GAUGE----out the GAUGE STUD----the pc board to the IVR CONTACT FINGERS-------through the IVR--------back out the IVR CONTACT FINGERS---------to the PC BOARD PIN------and to 12V POWER

That is the circuit path. ANY of the points and components along the way can be corroded/ broken/ not working/ etc.

You need a way to rig test resistors to check the gauge. Here is an edited photo someone made of the gauge tester



You can for example use substitution.........all three gauges are substantially the same. If the temp gauge is reading "so high" take jumper wires and jumper the oil sender wire over to the temp sender and see if the oil gauge now reads "the same" as the temp gauge just now did.

Be aware that gauges go bad, but more common, are---the studs get loose/ corroded, loosen/ tighten the gauge stud nuts several times to "scrub" the connections

Solder jumpers across the IVR connector fingers to the PC board traces

Replace the IVR with a solid state one

Check the PC board harness connector pins. Solder / fix them as necessary.

Keep in the back of your mind, the BULKHEAD CONNECTOR. The wire terminal through there could be loose/ corroded.

Mention of IVR fingers and their connection to the circuit board do not apply in this case. IVR is inside the fuel gauge.

Thanks for all the initial feedback.
Will read this more carefully later today.
All other gauges work, somewhat;
Fuel seems mostly OK, but can lose 1/4 tank between start cycles
Alternator seems spot on
Water Temp works, but is slow to react, that may be a thermostat issue though since I only get needle deflection when car is truly hot.

Cheers

Craig

and LOL
Agree with the statement about not needing a diagram for the PCB, easy to just follow the traces.

Ammeter is a completely different gauge. Redfish pointed out your IVR is inside the fuel gauge (Rally dash) So disregard the tripe about the contact fingers. But one thing I was attempting to point out is to follow the PATH, point by point, and don't disregard that one or more of those points can cause trouble.

Made a bit of progress.
Verified wire is good from sender to 9 pin circular connector.
Verified gauge worked by applying 0 - 5VDC and got 100% gauge deflection.
Removed sender from block and it ready steady 24 ohms despite applying up to 40 psi compressed air.
I have an old sender and it goes from ~ 80 ohms to 36 ohms when i apply up to 40 psi compressed air.

Looks like I need a sender.
Oh well, I'll take this opportunity to clean the inside of the gauge bezels and refresh the needles.

Now if I could only figure out how to remove the trip gauge reset knob.
Is it as simple as just pulling it off and re-gluing later???
I'll take a closer look.

Thanks for the help.

Dont reglue knob. If it ever has to come out again yer pooched.

The knob unscrews. Hold the shaft with a pair of needle nose pliers and it should come off.

You'll need to remove 2 screws from back of speedometer and carefully separate the housing and bezel with the speedometer still in the bezel. then you can hold the shaft and unscrew the trip knob. There is a rubber isolator at those 2 screws between speedometer and housing. Little rubber washer at that reset stem too. Be sure these are in place at reassembly.

long overdue update, cause I just had time to get back to this.

while the dash was out we took the time to "'refinish" the dash surround.

• sanded the "chrome" areas
• replaced the woodgrain with new aftermarket
• sprayed new Duplicolor chrome paint

It looks much better than before.
Also painted the gauge needles neon orange, tach needle came off during this process, but I think I got it back in place, (that's another thread).

Also cleaned up the heater box and associated bit.

I ended up snapping a pin on the PCB for the 9 pin connector, could have resoldered, but bought new aftermarket (heaterboxguy?). The PCBs seem well made and the 9 pin connector pins are much more robust than factory.

I started this project because oil pressure gauge was non-responsive.
IT NOW WORKS, but most likely because I also replaced the sender.
The sender that was on the car showed no resistance change when I pressurized it with air.
Constant 70 ohms or so.
The new sender varies from 70 - ~ 30 ohms when pressurized.

Sadly, the tach does not work.
I either didn't connect correctly, or the needle is not seated correctly.

Off to research correct wiring connections on back of tach, one eye connector on a post and one push on connector on a post.
really hoping it is wire error and not needle issue

sob.

Thanks for the earlier help.

Craig

Thanks for update. I know nothing of the internals of factory tachs. "They either work or don't" if wired correctly. There is / was an outfit that offered drop-in modernized PC boards for some tachs

By the way what ignition are you running. Tachs will not work with such as MSD/ CD type igntion, not without special adapters etc

Got lucky.
Found that the 12VDC input to the tach had come loose at the fusebox end.
SWEET!