Zig's gas gauge

Discussion in '1947-1954' started by Bill Hanlon, Nov 21, 2018.

  1. Bill Hanlon

    Bill Hanlon Member

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    Zig needs to get his gas gauge working.

    They are stock (1950?) GMC gauges, which means they were designed to work on 6 volt positive ground juice.

    The truck is now 12 volt negative ground. I'll need to do some investigating to find out how to get the positive ground gauge working in a negative ground system.

    Just a thought: Isn't the Chevy of the same year 6V negative ground? Maybe we could use a Chevy gas gauge? Is it the same color as the GMC gauge?

    There is some type of "reducer" attached to the voltage stud on the gauge. Zig: Is it a "Runtz"?
     
    Last edited: Nov 22, 2018
  2. Bill Hanlon

    Bill Hanlon Member

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    On Wed, Nov 21, 2018, 11:18 AM Bill Hanlon <bill_hanlon@comcast.net wrote:

    Your story at https://fifthaveinternetgarage.blogspot.com/2015/11/the-runtz-story_10.html mentions your interest in 1949 thru 1953 Chevy and GMC trucks. As you probably know, the GMC trucks of that era are positive ground. My friend is restoring (with a few mods) a ’50 GMC. He wants to use the stock gauge pod, but has already converted to 12V negative ground. I’m his electrical “expert”.


    Is there a solution available to get his 6V positive ground gas gauge working in a 12V negative ground system?


    Thanks for your time and effort.

    From: Randy Rundle [mailto:fifthavegarage@gmail.com]
    Sent: Wednesday, November 21, 2018 12:17 PM
    To: Bill Hanlon <bill_hanlon@comcast.net>
    Subject: Re: Email from blog


    Yes there is because he has already changed the polarity all he needs is the runtz for the fuel gauge and one for maybe the water temperature or pressure unless those are both mechanical and you'll be good to go

    On Wed, Nov 21, 2018, 12:34 PM Bill Hanlon <bill_hanlon@comcast.net wrote:
    Thanks for the quick response Randy. The ammeter doesn’t care and the temp and oil pressure gauges are mechanical.


    So the power side of the gas gauge gets the output end of the Runtz and the other side of the gauge still connects to the sending unit.


    From: Randy Rundle [mailto:fifthavegarage@gmail.com]
    Sent: Wednesday, November 21, 2018 12:47 PM
    To: Bill Hanlon <bill_hanlon@comcast.net>
    Subject: Re: Email from blog

    Yes... that's it.
     
    Last edited: Nov 21, 2018
  3. 52wasp

    52wasp Member

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    Bill,
    Although the gauge conversion doesn't apply to ME, I would like to Thank YOU for your effort!

    Happy Thanksgiving!

    Mike
     
  4. Zig

    Zig Member

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    AFF070A2-15C1-423C-B51F-D65929A4CDEA.jpeg D86CD07A-68B3-495C-BF96-B9559096A476.jpeg Absolutely!
    And yes, Happy Thanksgiving to all!
    Hopefully these photos will post right side up.
    Way back when, I had gone through and reworked the gauge faces to include the tan GMC gauge look.
    I don’t think I used a Runtz, but it at least was an equivalent.
    It is hooked to the empty side of the gauge.
    Wire harness is for stock GMC for these year trucks that I purchased through our host.
    Wire color looks correct for 12 volt negative ground?
     
  5. Bill Hanlon

    Bill Hanlon Member

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    Need to start by understanding a few things Paul.

    1. The picture above of the gauge faces shows zero oil pressure hinting that the engine is not running, but the ammeter shows serious charging. Was the key off when the picture was taken? Does the ammeter move as expected when the engine is running?

    2. What is the symptom of the gas gauge not working? Does it move at all? Is it stuck in some position? Does it only move 1/2 way?

    3. Are you using a stock gas tank?

    4. Are you using a stock sending unit inside the gas tank?

    5. Does the volt/ohm meter that Santa brought you still work?
     
    Last edited: Nov 26, 2018
  6. Zig

    Zig Member

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    Okay- sorry, it’s been a bit crazy around here...
    First, I believe when I took this photo, the 228 was not running. (So no oil pressure)
    Second: The gauge doesn’t move at all. No jump, bump, or flicker.
    I do have the stock tank (which now is finally through sending garbage out) and I had installed a new (stock) sending unit way back when.
    I got it from our host, and it was back when I still had 6volt service. (Not sure that that mattered)
    Finally, you better believe I have the volt meter that Santa brought! It doesn’t get any use because the last time I used it, everything was taken care of and has worked perfectly ever since. #cool#
     
  7. Bill Hanlon

    Bill Hanlon Member

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    This has nothing to do with the gas gauge, but I was just curious. Does the ammeter work otherwise? Turn on the headlights with the engine off. Does the ammeter move towards "D"? Turn off the lights, start the engine and rev it a little. Does the ammeter move towards "C"?


    For ease of troubleshooting it would be nice if the gas tank were about 1/2 full (optimist) or 1/2 empty (me).

    Gas gauge always at "E" means 1 of four things is happening.

    1. Gauge has no power.
    a. Set your meter to HIGH VOLTS.
    b. Connect the meter's black lead to a good ground.
    c. Turn on the key, but don't start the engine.
    d. Unless you are a lot younger and more limber you may need a helper for these tests as you will be up under the dash.
    e. Touch the meter's red lead to the end of the Runtz that connects to the gas gauge. It should read about 6 volts. What does yours read?
    f. Touch the meter's red lead to the other end of the Runtz. It should read about 12 volts. What does yours read?
    g. Is the black wire from the Runtz connected to a good ground?
    h. Turn off the key.

    2. Assuming #1 above gives good readings … maybe the wire between the gauge and the sending unit is shorted to ground.
    a. Remove the wire from the "F" side of the gas gauge.
    b. Turn the key on.
    c. The gauge should read full. What does yours read? If empty, the gauge is probably defective.
    d. Turn off the key.
    e. Set the meter to HIGH OHMS.
    f. Hold the meter's red lead to the meter's black lead and use the "ADJUST ZERO OHMS" knob to set the meter to zero.
    g. Touch the red meter lead to the wire you removed from the "F" side of the gauge. The meter should read somewhere between 30 ohms (full tank) and zero ohms (empty tank). Half tank should read near 15 ohms. What does yours read?

    3. Assuming #2 above gives good readings … maybe the wiring to the tank is shorted to ground.
    a. If 2.g above reads zero or near zero ohms
    i. remove the wire from the gas tank sending unit.
    ii. touch the red meter lead to the wire you removed from the sending unit. The meter should not move. What does yours do?
    iii. touch the red meter lead to the terminal on the sending unit. The meter should read the same as 2.g above. What does yours do?
    b. If 2.g above reads between 5 and 35 ohms and the gauge still reads E when all wiring is back in place the gauge is probably defective.

    4. Assuming 3.a.iii above reads zero ohms and there is gas in the tank... maybe the sending unit is defective.
    a. Remove the sending unit from the gas tank.
    b. Touch the black meter lead to the metal of the sending unit's mounting flange.
    c. Touch the red meter lead to the sending unit terminal.
    d. Move the float assembly up and down. When down the meter should read zero ohms. What does yours read?
    e. When up the meter should read 30 ohms ohms. What does yours read?
    f. If 4.d and 4.e both read correctly ….
    i. Attach wire removed in step 2.a
    ii. Attach wire removed in step 3.a.i
    iii. Attach a wire from the sending unit's mounting flange to a good ground.
    iv. Turn on the key.
    v. Move the float assembly up and down. The gas gauge should read F when the float is up and E when the float is down. What does yours read?
    vi. Turn off the key.

    If everything seems to check out OK, but the gauge is still stuck on E when you reinstall the sending unit and turn on the key, either the float has sunk or some part of the sending unit that shouldn't be is touching ground when it is installed.
     
    Last edited: Nov 28, 2018
  8. Bilbo1

    Bilbo1 Member

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    Hey Bill H, And Zig. From step 2g on down to 4b, the black wire should be connected to a good ground to get those readings. Otherwise the troubleshooting looks accurate.
     
  9. Bill Hanlon

    Bill Hanlon Member

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    Black wire that Mr. Brubaker refers to is the meter's black lead. Thanks for the review Bill.
     
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  10. vwnate1

    vwnate1 Member

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    Good old Randy Rundle .
     
  11. Zig

    Zig Member

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    70CD7DAA-46B7-449E-B545-358B57BDD827.jpeg
    Wow!!!
    Thank you Bill!!! Lots to check on, but I guess I won’t have a chance until Christmas break, the way things are going.
    BUT!!! I can’t wait to check this out and see if the gauge will come back to life!

    As far as the amp meter, I must have the wires on the wrong post as it goes toward “charge” when I turn on the lights. (Or even the key)

    Thanks again!!!
    Here’s (an upside down?) photo of the first vehicle I ever had. Never got it running, but I put lots of imaginary miles on it from behind the wheel.
    1952 Chevy Deluxe.
    It could have been a really cool car.
     
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  12. vwnate1

    vwnate1 Member

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    That's a sweetie right there, a BelAir by the looks of the backlight .
     
  13. Bill Hanlon

    Bill Hanlon Member

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    Good diagnosis Paul.
     

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