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Can a '40 Ford gas gauge work on 12v w/no reducer?

Discussion in 'The Hokey Ass Message Board' started by Just Jones, Mar 30, 2010.

  1. Just Jones
    Joined: Jan 11, 2005
    Posts: 928

    Just Jones
    Member

    Ok, stupid question of the day, but can I run the gas gauge in my '40 pickup on 12 volts without a voltage reducer? I was told that since the sending unit basically just acts like a switch that it wouldn't matter.

    But since I hate doing things like setting my own truck on fire due to dumbass wiring mistakes on my own part, I thought I'd ask here first . . .


    For what it is worth, I am hunting down a factory '60s Ford pickup reducer, but I need a gas gauge to get to Vegas for VLV this weekend.
     
    Last edited: Mar 31, 2010
  2. treb11
    Joined: Jan 21, 2006
    Posts: 3,519

    treb11
    ALLIANCE MEMBER

    it doesnt work like a switch (on /off) it works like a rheostat. different sending units operate at different ranges of resistance (Ohms) as long as the sending unit matches your gauge, GTG
     
  3. Just Jones
    Joined: Jan 11, 2005
    Posts: 928

    Just Jones
    Member

    ok, so I have the original sender in the tank and original gauge . . . and I get what you mean about the sender being a rheostat that the gauge reads from ...

    . . . but can I run it on a 12 volt system without a reducer?
     
  4. Just Jones
    Joined: Jan 11, 2005
    Posts: 928

    Just Jones
    Member

    . . . or maybe if GTG means "good to go" then you already told me.

    Is that like that new crazy texting language all them young whipersnappers are using these days??
     
    Last edited: Mar 30, 2010
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  5. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 5,072

    Ebbsspeed
    ALLIANCE MEMBER

    Speedy, the picture in your avatar is nuts. Are those two cars still moving, or is that the way they ended up after the accident? I suspect that at least one of the drivers needed to towel off the seat.....

    As far as the gas gauge, I'd be real tempted to use a resistor or regulator to drop the voltage to 6 volts. As designed, the gauge and sender are each engineered to have anywhere from a 0 to 6 volt drop across their windings. In other words, when the sending unit is at it's lowest resistance, (assume 0 Ohms) then there is a 6-volt drop across the gauge, and results in a full reading. Now let's plug 12 volts into the equation. At what position is there going to be a 6-volt drop across the gauge? Probably about the same time that the other 6 volts is dropped across the sending unit, ie half a tank. So it could be that, as you blissfully drive over to Vegas for VLV, your gauge will show a full tank and you only have half.
     
  6. Just Jones
    Joined: Jan 11, 2005
    Posts: 928

    Just Jones
    Member

    Hey Ebb - That picture was taken at the Saugas Speedway back in the late 40s -early 50s, I am told. I would imagine there are guys on the HAMB who even know who those drivers are, but my understanding is that picture was taken in motion, and that both drivers walked away . . . or something like that.

    Thanks for the info on the gas gauge. Actually, what you said about the gauge probably reading double (half a tank = full reading) makes a lot of sense. But I guess that wouldn't be all bad, as when it gets down to around half it would mean almost empty, right?

    I know this is not the best way to go, but it may help me keep from running out of gas on the way to Vegas. I appreciate the info big-time.
     
  7. clifforddean
    Joined: Mar 3, 2009
    Posts: 101

    clifforddean
    Member

    I converted my 49' Ford to 12 volt neg. ground and did not have to do a thing to gas gauge it works just fine. I know of a couple guys doing the same thing and not having a problem.
     
  8. Just Jones
    Joined: Jan 11, 2005
    Posts: 928

    Just Jones
    Member

    Cool! I'm on it! That makes my freakin day. Off to the garage . . .
     
  9. 70elim
    Joined: Jan 3, 2010
    Posts: 28

    70elim
    Member
    from PA

    There are vendors Carpenter for example who sell a float/sending unit that is made specifically for the stock gauge. It is used when converting to 12vt. and you must use the stock gas gauge. Mine works fine.
     
  10. blown49
    Joined: Jul 25, 2004
    Posts: 2,213

    blown49
    Member Emeritus

    Not really true on the Ford gauges. Sending unit has a bi-metal strip with a coil of wire wrapped around it and a set of contacts. Dash gauge also has a bi-metal strip also with a coil of wire around it but no contacts. As the float changes the contacts open and close to change the current through the loop. NAPA has a voltage reducer part #VT6187 (around $8.00) that will work to drop to 6V..

    See following print for details of fuel gauge:

    [​IMG]
     
  11. Just Jones
    Joined: Jan 11, 2005
    Posts: 928

    Just Jones
    Member

    Thanks for the diagram Blown 49 . . . so, if I am reading this diagram correctly, these gauges are positive ground?

    Also, thanks for the alternative NAPA part information. I am assuming that this is not a voltage reducer that would supply 6V to all gauges like the '60s-70s Ford part I mentioned above (NAPA - Echlin IR-1, about $52)? This would be an inline reducer, used individually for each gauge, like those RUNTZ things that Speedway sells?
     
  12. no55mad
    Joined: Dec 15, 2006
    Posts: 1,851

    no55mad
    ALLIANCE MEMBER
    from nipomo, ca

    Someone on Ebay sells the reducer for this conversion. They are ~ $8 and one is required for each gauge. Go to Ebay motors and search 'voltage reducer'.
     
  13. blown49
    Joined: Jul 25, 2004
    Posts: 2,213

    blown49
    Member Emeritus

    Originally Positive ground but will work on negative ground as well. The NAPA VT6187 can feed all three gauges from one VT6187 (Oil, Temp & Tank (don't need one fore amps). Just run a wire from the ignition switch to the reducer. Other side of the reducer to one gauge then jump wire to next gauge and then repeat untill all three gauges are fed.

    Jim
     
  14. Just Jones
    Joined: Jan 11, 2005
    Posts: 928

    Just Jones
    Member

    Thanks again, Blown. I'm calling my friendly neighborhood NAPA boys right now . . .and that diagram was a great help as well.
     
  15. AnimalAin
    Joined: Jul 20, 2002
    Posts: 3,417

    AnimalAin
    Member

    My roadster has had a busted fuel gauge for some time now. I should probably fix it, but it hasn't risen on the prority list yet. In town, I check the fuel level with a wooden dowel every so often before leaving the garage; on the road, I use a rule of thumb of six gallons per hour on the freeway. If your coupe has a stock gas tank, that should be about two hours driving time, with a couple of gallons reserve.

    I have run this car out of gas several times (idiot driver), but oddly enough, not once since the gas gauge broke.
     

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