'97 Ram 1500 tachometer not working

Discussion in 'General Discussion' started by mplipp, Dec 23, 2016.

  1. mplipp

    mplipp Junior Member

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    Ram Year:
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    Engine:
    5.2L
    Wasn't sure if this qualified as "Engine/Performance" or "Tech" so I'll start here. I'm a carpenter with some downtime over the holidays and figured I'd do some work on my gopher truck. While I'm waiting for my new body parts to arrive...

    The tachometer has never worked in my truck (I bought it used) and my old mechanic said he couldn't find a mechanical problem and said it was most likely the gauge. I found a used one and swapped out the whole cluster but no luck - all the other functions (fuel, temp, press, speedo) work on both clusters. I have a hard time believing the used one coincidentally has only the same non-working gauge as my original. From what I could find on the internet, the tach gets its signal (increasing voltage=higher rpm) from the top of the coil that goes to pin 31 on the 3rd harness at the control module on the firewall. I can't find any docs to figure out where it goes from there and the pinouts I could find for the black and white connectors into the back of the cluster make no mention of the tach signal. Any ideas???
     
  2. dudeman2009

    dudeman2009 Senior Member

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    Engine:
    Magnum 360
    First, run a cluster check. With the key off hold down the trip reset button, then turn the key to run and wait for the work 'check' to appear on the odometer. Then you can release the trip reset switch and the cluster will take about a minute to do a full self test. You will know if the tach is damaged in the cluster as the needle will not move.

    Try that and if the gauge is good, i'll look up in the wiring diagrams where it gets its tach signal from.
     
  3. mplipp

    mplipp Junior Member

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    I saw that procedure posted in a couple of places but wasn't sure if it would work on mine - the 1997 model has a mechanical odometer. If it will still trigger a cluster gauge check without the odometer display, I will certainly try it because the needle should still move if the mechanical portion is okay and it simulates a signal (voltage?). If I knew which pin carried the signal, in theory I should be able to pull the cluster back out, put DC current across that contact and the ground pin and get the tach needle to move. That would tell me the gauge is working and I would need to trace the signal wire back from the dash.

    On a related subject, any idea where I could find better schematics than the Chilton manual I have? While I had the dash apart I noticed a couple of spliced wires and wanted to undo whatever "rig" the previous owner did. For example the horn has been replaced with an aftermarket on a toggle switch (the stock horn is missing and I am hoping the original harness is still there so I can just get a used stock one to put back).

    Another issue I saw is the wire coming off of the AC compressor (top, right) has been cut, split/spliced, and then the rigged splices have been cut and just left there. Obviously something didn't work and the attempt to get around it didn't work either. I'm trying to figure out where that wire is supposed to go, put it back, and fix whatever relay or component originally failed. I believe there should be a lead off the compressor over to the control module - the other side of the circuit from the high/low pressure switches?

    I appreciate your reply.
     
  4. mplipp

    mplipp Junior Member

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    Cluster testing question

    I found this pinout (below) for harness A (black) and stripped the ground (9), tach (3), oil press (10), and fuel (11) wires from the clipped male harness that came with the used cluster gauge. When I put a 9V battery across the ground and the signal lead for a few of the gauges, I can get the oil pressure and fuel needles to move. However, 9V positive on pin 3 and 9V negative on pin 9 does not get the tach needle to move. I'm sure this isn't an ideal test but I got two gauges to work and they were correctly labeled according to the pinout I found. Therefore, I assume pin 3 is the signal wire for the tach but unsure how to do a good test. Any suggestions?

    1-Illumination (Dimmer)
    2-
    3-Tachometer
    4-Oil Pressure
    5-Maintenance Required
    6-Check Engine
    7-Low Washer Fluid
    8-12 Volts from Fuse 12 in FUSEBLOCK (Power for Lamps)
    9-Ground
    10-Oil Pressure
    11-Fuel
    12-
    13-4WD
    14-Check Anti-lock
     
    V10so_utah likes this.
  5. dudeman2009

    dudeman2009 Senior Member

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    Engine:
    Magnum 360
    For your wiring diagrams, this is a link to the 96-97 service manual: https://1drv.ms/b/s!AivLG2b81LJSi-BbWj4qRiX_PbVllg

    As for the gauge, I think the needle portions were still servo actuated via ICs on the cluster, i'm not 100% though.

    As for undoing another mans garbage electrical hodge podge, I wish the best of luck to you. Its one thing to troubleshoot electrical, its another to try that with another persons bullshit in the way.

    If you cant easily tell what they were trying to do, it MIGHT be easier to systematically pull everything they did and replace it with the factory wiring according to the service manual.
     
  6. mplipp

    mplipp Junior Member

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    Thank you!

    I can't say thank you enough for the link - being able to reference the factory setup is invaluable. I was able to find a few of the factory connectors at the used part lot this morning and started replacing the spices. I agree that it will be easier to put it back to original and then start troubleshooting each item.

    I did check for current across pins 3 and 9 (tach, ground) at the cluster with the engine running with no luck. After referencing your manual, I can check output at pin 31(C) at the control module, and then check for continuity at the cluster harness.

    On a more positive note, some body parts arrived today so I may have a more productive day tomorrow :^)

    Thanks again, I really appreciate the help.
     

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