Very strange electrical issue

Discussion in 'General IH Tech' started by TheScoutMaster, Jun 21, 2015.


  1. TheScoutMaster

    TheScoutMaster High Wheeler

    Joined:
    Aug 1, 2002
    Messages:
    2,127
    Likes Received:
    35
    Trophy Points:
    48
    Location:
    70 Miles North of Hell
    On my 74 SII rebuild. Still doing body work, and run it every time I work on it for a few minutes. Both batteries are charged, tested, and basically brand new. Anyways, I replaced ALL the gauges with after market, tying them all in to the original sending units, if required. The issue I am having is between the horn and the fuel gauge. Since I have a detachable steering wheel, I mounted the horn on the dash via a push button. I have four buss bars tucked behind the dash on the inside firewall- one is solely ground for all gauges and components, the other is solely batt 12 volt for radio, acc, etc. The third is solely ign on. The fourth is solely lights activated on - coming off the light switch - powering gauges/radio that have dim feature.

    The push button goes from the 12v batt to the horn relay to the horn and grounds at the horn. The fuel gauge is connected to the original sending unit wire and is working, 12v goes to ign only buss bar, ground buss bar, and light (dim) buss bar.

    Never noticing it before today, if you turn the ign key all gauges come on - as supposed to. The fuel gauge reads how much I have, which I believe to be accurate since the percentage has been dropping between filling up, breaking in new engine and running periodically at shop. When I hit the horn button I notice that the fuel gauge (reading the correct amount) "trips" showing zero, then goes back to showing the correct amount. It seems that the action is in conjunction with the horn relay in the engine compartment. It seems to also happen when you let your finger off the push button, especially if you hit the button really quick (before horn can sound)...

    I cannot figure out what the hell is happening. Not worth pulling the entire dash - I can live with it, but was wondering what might be going on? No shorts, nothing, everything was meticulously wired, and double checked. Disconnected the ground from the horn, still happens, disconnected the hot going to the horn, still happens, the only thing being actuated is the relay which seems to be "tripping" the gauge momentarily before showing the correct amount.

    Thoughts? Thanks.
     
    Last edited: Jun 21, 2015
  2. kevingweq

    kevingweq Y-Block King

    Joined:
    Nov 1, 2013
    Messages:
    3,177
    Likes Received:
    781
    Trophy Points:
    113
    Location:
    Royalston
    If I am understanding you correctly , You are supplying power to the horn relay to activate it ??

    Horn relay should be powered at all times and the horn button should supply the ground to activate the relay
     
  3. TheScoutMaster

    TheScoutMaster High Wheeler

    Joined:
    Aug 1, 2002
    Messages:
    2,127
    Likes Received:
    35
    Trophy Points:
    48
    Location:
    70 Miles North of Hell
    My mistake. Wrote my post wrong. The horn is the original lead going to the steering wheel and basically I put a push button in between...
     
  4. TheScoutMaster

    TheScoutMaster High Wheeler

    Joined:
    Aug 1, 2002
    Messages:
    2,127
    Likes Received:
    35
    Trophy Points:
    48
    Location:
    70 Miles North of Hell
    Could the ground from the horn button be interfering with the ground of the gauge? Very weird... if the grounds were spliced together would it be affecting this?
     
  5. TheScoutMaster

    TheScoutMaster High Wheeler

    Joined:
    Aug 1, 2002
    Messages:
    2,127
    Likes Received:
    35
    Trophy Points:
    48
    Location:
    70 Miles North of Hell
    I'm now starting to wonder if I spliced in the ground of the horn to the ground of the gauge, as silly as that may sound. Would that cause the issue I may be experiencing if the sending unit momentarily went to ground? Damn, will pull the dash bezel off this coming weekend to double check what is going on... all the components had their own ground, but if I remember correctly I added an additional gauge and may have spliced into an existing ground so as not to have to run a new wire to the buss bar...
     
  6. Tim Potter

    Tim Potter High Wheeler

    Joined:
    Aug 6, 2002
    Messages:
    2,708
    Likes Received:
    14
    Trophy Points:
    38
    Location:
    La Habra, Ca
    what would make more sense is if you mistakenly spliced the horn ground into the fuel gauge signal wire. but, it makes no sense for you to splice the horn ground into anything since you went to the trouble of installing a ground buss.
     
  7. 2dafloor

    2dafloor Farmall Cub

    Joined:
    Dec 9, 2012
    Messages:
    166
    Likes Received:
    13
    Trophy Points:
    18
    Location:
    knoxville
    Im thinking all the separate grounds you have created a grounding offset. its common in DC.
     
  8. TheScoutMaster

    TheScoutMaster High Wheeler

    Joined:
    Aug 1, 2002
    Messages:
    2,127
    Likes Received:
    35
    Trophy Points:
    48
    Location:
    70 Miles North of Hell
    The buss bar holds all the grounds from all cab devices, and the buss bar itself grounds to one point, including engine ground strap, batteries, etc. Basically, everything grounds to one location.
     
  9. TheScoutMaster

    TheScoutMaster High Wheeler

    Joined:
    Aug 1, 2002
    Messages:
    2,127
    Likes Received:
    35
    Trophy Points:
    48
    Location:
    70 Miles North of Hell
    If I accidentally grounded to the sensor wire, what would ohm value (outside of the 10-73) be for grounding out the circuit? Would it drop to zero?
     
  10. TheScoutMaster

    TheScoutMaster High Wheeler

    Joined:
    Aug 1, 2002
    Messages:
    2,127
    Likes Received:
    35
    Trophy Points:
    48
    Location:
    70 Miles North of Hell
    Ok. Pulled the dash and tested the gauge while in - tested all wires while honking the horn. Disconnected the sending unit wire and hooked up a volt/ohm meter, ohms stayed stable, no fluctuations - put gauge still "tripped". Pulled the ign power supply and ran to another power source, gauge "tripped". Pulled ground and grounded to different good ground point, same thing. pulled light (dim) wire and left off, gauge still "tripped". Is it possible that the gauge might be extremely sensitive, or something wrong with the horn relay? Every time I honk the horn and the relay engages the gauge trips (will show fuel level, momentarily drop to zero and go back up to what it was before). Very weird. May swap out the horn relay and see if things change...
     
  11. kevingweq

    kevingweq Y-Block King

    Joined:
    Nov 1, 2013
    Messages:
    3,177
    Likes Received:
    781
    Trophy Points:
    113
    Location:
    Royalston
    When you disconnected the sender wire , there was only one wire left connected to the gauge correct ?? Which would be power from key switch ?
     
    Last edited: Jun 29, 2015
  12. TheScoutMaster

    TheScoutMaster High Wheeler

    Joined:
    Aug 1, 2002
    Messages:
    2,127
    Likes Received:
    35
    Trophy Points:
    48
    Location:
    70 Miles North of Hell
    The gauge has 4 wires (12v ign, ground, sender, 12v lights/dim). I pulled each wire and tested the wire that I pulled reading what happened on the voltmeter when pushing the horn button. In each instance the gauge acted up with nothing showing to be suspicious on the meter (ie voltage drop, ohm drop/increase, ground issues, etc). I wonder if the horn relay could be an issue somehow?
     
  13. kevingweq

    kevingweq Y-Block King

    Joined:
    Nov 1, 2013
    Messages:
    3,177
    Likes Received:
    781
    Trophy Points:
    113
    Location:
    Royalston
    What happens when you pull the gauge out of the dash with just a power wire and sender wire hooked up ??

    Anything is possible , But the horn relay should not have any effect on that circuit unless wired incorrectly .
    Have you seen any evidence of melted wires ??
     
  14. kevingweq

    kevingweq Y-Block King

    Joined:
    Nov 1, 2013
    Messages:
    3,177
    Likes Received:
    781
    Trophy Points:
    113
    Location:
    Royalston
    2da floor , Could you explain this grounding offset phenomena ?? I am curious
     
  15. TheScoutMaster

    TheScoutMaster High Wheeler

    Joined:
    Aug 1, 2002
    Messages:
    2,127
    Likes Received:
    35
    Trophy Points:
    48
    Location:
    70 Miles North of Hell
    No melted wires. I do not believe I have a ground loop. I grounded directly to battery and it still caused the issue. I wonder if the gauge is extremely sensitive? Maybe due to a voltage drop issue with the horn relay engaging? I don't know... probably not worth me exploring any deeper as taking the dash off was a b1tch.
     
  16. Eric VanBuren

    Eric VanBuren Lives in an IH Dealership

    Joined:
    May 7, 2004
    Messages:
    6,011
    Likes Received:
    26
    Trophy Points:
    38
    Location:
    Maple Valley , Wa
    The problem is your gauge unless your battery is really really discharged. The horn relay has nothing to do with it. If anything it would be the horn that caused the problem but if there was a problem with the horn that caused the battery voltage of a good battery to sag enough to effect the gauges you would have smoking, melted wires.
     
  17. 2dafloor

    2dafloor Farmall Cub

    Joined:
    Dec 9, 2012
    Messages:
    166
    Likes Received:
    13
    Trophy Points:
    18
    Location:
    knoxville
    Not very well I'm neither an EE nor did I stay at a Holiday inn lately.

    I tried to wire up a wideband O2 sensor using the power as the cigarette lighter so I could move it to other vehicles as need and I got some strange reading with it hooked that way.

    http://www.innovatemotorsports.com/resources/grounding.php

    Its fairly common in industry where there is a mix of 24 volts DC for controls,like operator push buttons, and AC drives etc for motor control, and communication like Device net(canbus) etc.
     
  18. TheScoutMaster

    TheScoutMaster High Wheeler

    Joined:
    Aug 1, 2002
    Messages:
    2,127
    Likes Received:
    35
    Trophy Points:
    48
    Location:
    70 Miles North of Hell
    Reviving this old post. Still have the issue with the horn "resetting" the fuel gauge. I have literally triple checked everything and cannot figure out why this is happening. Could the 12v to horn relay be the issue? Thoughts? Thanks.
     
  19. TheScoutMaster

    TheScoutMaster High Wheeler

    Joined:
    Aug 1, 2002
    Messages:
    2,127
    Likes Received:
    35
    Trophy Points:
    48
    Location:
    70 Miles North of Hell
    I wonder if the horn relay, which I assume is running off the ignition on circuit, is momentarily pulling so much that it is robbing voltage from the ignition buss bar (tapped main ignition on wire to this ignition buss bar for components) and thus the trip? Anyway to check this theory out at the fuse panel? If I pull the horn fuse and the problem goes away, does that tell me anything? If so, alternative method to power the horn circuit to avoid gauge tripping? I assume the Scout II relay is the same as this:

    [​IMG]
     
    Last edited: May 29, 2016
  20. scoutboy74

    scoutboy74 Lives in an IH Dealership

    Joined:
    Mar 10, 2004
    Messages:
    6,712
    Likes Received:
    1,160
    Trophy Points:
    113
    Location:
    Daze Crick, Jefferson
    The power supply to the horn relay isn't switched, unless its been modified that way.
     

Share This Page