how to bench test a 70 Dart instrument cluster?

str12-340

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I have been completely rebuilding a 1970 Dart including all new electrical.

Of course the one thing that didn't work in the whole electrical system is the thing that is most difficult to get to - the instrument cluster. Everything on the right side works fine, the dash lights work fine all across. What doesn't work are the 2 gauges on the left - gas and temp. These are the two gauges that go through a voltage limiter. The gauges, circuit board and the voltage limiter (modern version from RTE) are all new. There is 12 volts at the wire that supplies the voltage limiter and then the gauges. You can hardly get to anything from under the dash. I pulled the cluster out again today to figure it out.

As far as I can tell all it could be is the voltage limiter, the circuit board or the gauges. Gauges are buried to the left with gas in the tank and the engine up to temp (using a heat sensor gun). I'm hoping someone can help with some advice on how to bench test this stuff: what do you use as a power supply? RTE gave me instructions for testing the voltage limiter out of the cluster using an led that is part of the limiter. I can't figure out how to test the gauges on a bench, especially since power has to go through the limiter which evidently pulses to replicate the points in the original.

Any suggestions would be appreciated
 

67Dart273

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Easy. Identify the pin supplying 12V from the key (and you likely have, and apply battery power to it.

The cluster is "poorly" grounded, OEM, through mounting screws. Put a wire pigtal under one of the common ground screws, and screw it to your dash frame or column support, when installing dash. Use that pigtail, of course, for the test ground.

With no power, carefully inspect and check resistance from the PC board pins to the IVR contacts. Check carefully from the board traces to the actual contacts. These fail, and it is wise to solder jumper bridges across from the traces to the IVR contacts. Also work the IVR in/ out a few times to "scrub" the contacts

The gauge studs can lose contact with the "eyelet" contacts on the PC board. Work the nuts loose/ tight/ loose/ tight a few times to scrub them. Consider replacing the nuts with "real" nuts

Rig appropriate test resistances from the sensor terminals to ground, and see if the gauges follow. They are same resistance regardless, of fuel, temp, or oil, if equipped

Check the harness connector pins carefully on the board for loose. You can clean them and solder them to the board.
 

str12-340

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So the cluster is out of the dash, Can I just use a 12v lantern battery from the hardware store to supply power? Can I just ground it to something big and metal in the shop (like a 700 lb metal shelf unit?).

Rig appropriate test resistances from the sensor terminals to ground, and see if the gauges follow.

How do you do that? I have a "multi-tester" but have never used it except to measure voltage. I don't really understand the concept of varying test resistances.
 

Dana67Dart

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Post a photo of your temp and fuel gauge.

I know it is corney but watch this video 2 or 3 times

 
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67Dart273

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I don't know if a lantern battery is stable enough under current. I'd use a car battery

Ground LOL. NO this isn't a crystal radio. The ground means the NEG side of the battery. The cluster is originally poorly grounded to the car dash/ body/ column support "which is" battery negative. So you add a pigtail to the PC board screws (traces the traces, they go to the ground side of the illumination lamp sockets) Add a wire, and that is your "battery neg"
 

67Dart273

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Varying test resistances.......this has been posted many times.......

This photo came from an aftermarket "copy" of the OEM gauge test box, which is simply 3 resistances. They check if the gauges go to "1st mark," middle of scale, and "full" mark

So you need something that is either these three resistors or a variable (rheostat) such as a spare fuel tank sender, which you can set with your ohmeter

The three resistors are in YELLOW

c-3826-jpg-jpg-jpg.jpg



Now what you're functionally testing is the complete circuit path which is as follows in your test set up:

From POS post of battery---to ignition "run" pin of PC board harness connector----to board trace to IVR unit---via board traces to the oil and fuel gauges---through the gauge---out on the board trace and to the PC board connector pin for the oil or the fuel sender---connect your resistor----to ground........and back to battery negative

The current through the resistor--more current for a lower resistor, causes the gauge to read HIGHER on the scale.
 

Dana67Dart

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Here is the back side of the passanger side cluster cir board as seen from the front of the car.


  1. Yellow X is oil pressure light
  2. Green Xs are instrument panel lighting
  3. Fuchsia X is the right turn signal indicator light
  4. Blue X is the high beam indicator light.
  5. Red Xs are where the Amp meter passed through the cir board. (It is completely insulated from the cir board)
  6. White dots are cir board ground points
  7. 2 red dots are the input and output for the oil indicator lamp. yellow
  8. Yellow dot is 12 volt input for instrument panel illumination
  9. Green dot is 12 volt input for the right turn signal indicator
  10. Blue dot is 12 volt input for the right turn signal indicator
The following assumes the cir boards are still attached to your cluster

To test any all of the light bulbs EXCEPT the Oil light Indicator do the following:
  1. Get a 12V power source (car battery, 12V DC power supply, 12V lantern battery)
  2. Get or make some wires with alligator clips on both ends
  3. Connect the negative of the power source to the metal of the cluster, there is a spring metal clip on the back of the cluster by the speed cable connection that would do fine
  4. Connect the positive side of the power source to pin with the blue dot, the high beam light bulb should light up
  5. Connect the positive side of the power source to pin with the green dot, the right turn signal indicator light bulb should light up
  6. Connect the positive side of the power source to pin with the yellow dot, the instrument panel light bulbs should light up
To test the Oil indicator light
  1. Remove the negative of the power source from the metal of the cluster
  2. Attach the negative of the power source to one of the pins with the red dot
  3. Attach the Positive of the power source to the other pin with the red dot, the oil light should light up
For now we are going to leave the ammeter alone. (By the way, the posts on the ammeter, if rotated, WILL short the ammeter to ground causing an electrical melt down of the wiring in your car)

The Gauge posts are also sensitive to rotation. I damaged an otherwise good gauge by un-screwing the nut on the back. the nut was corroded enough that the post spun runinig the gauge. after that I use two gam nuts on the post before starting to loosen the nuts. then take off the jam nuts than remove the gauge nut


PXL_20221124_051855073~2.jpg



Here is the back side of the Drivers side cluster cir board as seen from the front of the car.


  1. Yellow X is Fuel Gauge Sender input
  2. Blue X is the Temp Gauge Sender input
  3. Red and yellow Xs are the approximately 5V output from the IVR and the input to the two gauges
  4. Red X is the 12V feed to the IVR
  5. White X and Dots are ground points
  6. Green Xs are the instrument panel illumination bulbs
  7. Fuchsia X is the drivers side turn signal indicator bulb
  8. Green dot is the instrument panel illumination bulbs 12V input pin
  9. Fuchsia dot is the drivers side turn signal indicator bulb 12V input pin
  10. Red dot is the IVR 12V input pin
  11. Yellow dot is input from the Fuel Sender to the Fuel gauge
  12. Blue dot is the input from the temperature sender to the temp gauge
The following assumes the cir boards are still attached to your cluster

To test any all of the light bulbs do the following:
  1. Get a 12V power source (car battery, 12V DC power supply, 12V lantern battery)
  2. Get or make some wires with alligator clips on both ends
  3. Connect the negative of the power source to the metal of the cluster, there is a spring metal clip on the back of the cluster by the speed cable connection that would do fine
  4. Connect the positive side of the power source to pin with the fuchsia dot, the drivers side turn signal indicator light bulb should light up
  5. Connect the positive side of the power source to pin with the green dot, the instrument panel light bulbs should light up

To test the gauges ( more complicated) do the following:

  1. Get a 12V power source (car battery, 12V DC power supply, 12V lantern battery)
  2. Get or make some wires with alligator clips on both ends
  3. Connect the negative of the power source to the metal of the cluster, there is a spring metal clip on the back of the cluster by the speed cable connection that would do fine
  4. connect the positive side of your power source to the pin with the red dot
  5. With your multimeter check voltage from ground to the red and yellow Xs, you should see a fluctuating voltage (it should not read 12V) it will typically read 3V,7V,5V,6V it will be all over the place (there is anther way to check this but for now this will do) the nominal voltage is 5-6V
  6. Here is where it gets complicated...
  7. You will need a resister or 3, as 67Dart273 showed, the low, half and high gauge readings need the following resistance values to make the gauges needles move. approximately 10, 23 and 74 ohms. (NOTE: The resisters should be a minimum of 1 watt) The actual values are not too important as long as they are close like 10 25 and 75 would work. You could get 1x 50 Ohm, 2X 10 ohm and 1x 5 ohm and make close enough to the needed resistance values
  8. With the power source hooked up as in step 1, 2, 3, 4 connect one end of a resister to a jumper wire and connect the other end of the jumper wire to the metal of the cluster. The same place you hooked the negative battery in step 3 is perfect.
  9. With another jumper wire connect the other end of the resister to the yellow pin OR the yellow X (NOTE when attaching to the ins be sure not to touch the pins next to the pin you are testing)
  10. This will test your fuel gauge. If you used the 10 Ohm resister the gauge should read Full or very close to or just over Full
  11. With the 23 Ohm resister the gauge should read about half
  12. With the 74 Ohm it should read empty
  13. To test the Temp gauge follow steps 1 thru 9 BUT attach to the yellow X or the pin with the yellow dot


There are multiple failure points along the way like pins on the cir board that are not making connections or the nuts on the gauges with bad connections, bad IVR, bad gauges.


so do your testing and report back.


AS THE VIDEO SAYS.... If you short the gauge sender inputs you will fry the gauges. if you had an older style mechinical IVR and you did not ground the cluster you will fry the gauges (thats why My dart is up on blocks right now.)




PXL_20221124_051841568~2.jpg
 
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str12-340

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thanks Dana, I watched it once and will watch it again in the morning and I'll take some gauge pics then too and post them. This is a standard dash (long flat speedometer) so the IVR is plugged into the back and according to the FSM and tracing the circuit board the IVR only feeds the two non-functioning gauges (temp and fuel). Oil pressure is split with the original light functioning as it should and a mechanical gauge under the dash. The ammeter wires are disconnected from the dash unit and feed an ammeter gauge under the dash (along with a voltmeter independently wired). From the video it seems to be the voltage limiter that is the culprit since both the gauges that it feeds act the same. I don't think it is the IVR ground since the limiter ground uses the same ground circuit as the dash lights and they work properly. I'll follow the directions RTE sent to test the IVR.

Back to a previous question: Can I use a 12V lantern battery to power the cluster on the bench? what would I use as a ground?

I'm starting to really understand how this stuff works (THANKS!), but still don't understand how to mimic the resistance at the sending unit to check the gauges. This is resistance in the flow to ground, correct? OOPS OUR POSTS CROSSED - is there a place to buy one of the 3 resistor boxes?
 
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str12-340

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sounds like it would be better to just pull an card table up to the fender and use wires to the Pos and Neg battery posts to power and ground the unit on the table. One problem that I have is that the IVR cannot be removed from the cluster without removing the cluster from the dash, the damned thing is right in front of part of the column/brake mount structure.
 

67Dart273

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I would look around like Mouser electronics, digikey, etc, and get some 2 watt or larger resistors as close as you an to the resistances listed.

One of the test boxes will cost MONEY and all they are, is a 3 position switch connected to 3 resistors.
 

Dana67Dart

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Back to a previous question: Can I use a 12V lantern battery to power the cluster on the bench? what would I use as a ground?

If you are talking one of those Big Square 12V batteries I say yes, you are not testing a large load.

1669274028471.png

Test leads ( you will need 4)

1669274173956.png


10 ohm 1 watt resister
1669274331376.png


10 ohm 5 watt resister
1669274386538.png



As for ground... your thinking earth ground like for an AC system in your house. The term "ground" and "negative" are used interchangeably. The negative post on the battery is the ground, if it is attached to the metal of the gauge cluster, the cluster is "grounded" and any wire you attach to the metal will also be grounded.


I'm starting to really understand how this stuff works (THANKS!), but still don't understand how to mimic the resistance at the sending unit to check the gauges. This is resistance in the flow to ground, correct?
1669273885479 (1).png
 
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Dana67Dart

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sounds like it would be better to just pull an card table up to the fender and use wires to the Pos and Neg battery posts to power and ground the unit on the table. One problem that I have is that the IVR cannot be removed from the cluster without removing the cluster from the dash, the damned thing is right in front of part of the column/brake mount structure.
You said "Bench Test" that sugests that the cluster is out.

I can tell you that removing the cluster is NOT for the faint of heart, I just got mine back in tonight. So if it is NOT out of the car you can still do all of the tests listed but will need to go about it a little differently.

You will need test leads like this to probe into the terminals and posts.
1669275245671.png



and the IVR CAN be removed from the cluster while it is in the car. I did it on the side of the road when mine failed.


If you are doing these tests PULL THE FRONT SEAT/ SEATS OUT. You will thank me!
 

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On my 65 coronet, ten years ago, I was having all kinds of electrical gremlins that were causing crazy issues, especially with high humidity. After many hours of testing I tracked it down to the original printed circuit board. I confirmed it being the problem by removing it and replacing it with a custom made wire harness. Right now I'm in the process of making a custom wiring harness and updating some things. I plan on replacing the printed circuit board with a new one, now they are available.
 

str12-340

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turned out in the end to be 2 things - the original transistorized IVR (voltage limiter) that I got with the new circuit boards from Charger Specialties was toast. fortunately it has a test light built in so finding it faulty was easy. With a new IVR from RTE that tested correctly, I found out the new fangled gauge replacements that I got from Herbs did not work even with the good transistorized IVR, but a pair of 52 year old gauges worked just fine. All the gauges are working fine now. We'll see if Herbs and Charger Specialties will take the non-working stuff back. (by the way the temp gauge from Herbs had the scale printed too high on the gauge face - something not obvious until the whole unit was put together)

One of the most important diagnostics tools that Dana67Dart put me on to was using a gas tank sending unit to test proper function of the gauges on a table before installing instrument cluster in the car. There is a diagram in post #11 and you just hook the sender up in series where it shows resistor in top right corner (brown). Move the float up and down to check gauge response. works on both the fuel and temp gauges. Top of post #11 shows the 12v battery I used to do the diagnostics out of the car. I would also recommend really absorbing the basics in the ancient video in post #4 - it really gave me a basic understanding of the system before I blundered forward any farther.
 

Dana67Dart

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(by the way the temp gauge from Herbs had the scale printed too high on the gauge face - something not obvious until the whole unit was put together

That is too bad. I don't understand why repo companies make such mistakes.




One of the most important diagnostics tools that Dana67Dart put me on to was using a gas tank sending unit to test proper function of the gauges
Thanks for the shout out but it was 67Dart273 who mentioned about the sender
So you need something that is either these three resistors or a variable (rheostat) such as a spare fuel tank sender, which you can set with your ohmeter
 
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