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Technical *TECH* Make a Gauge Tester/What-Sender-will-work-with-my-dumb-gauge Thingie

Discussion in 'Traditional Hot Rods' started by Dreddybear, Feb 6, 2014.

  1. Dreddybear
    Joined: Mar 31, 2007
    Posts: 5,982


    So you ever find a cool gauge but want to test it? Ever wonder what sender you need to find to make those old gauges work right? The time has come to make a STAND! Let those old stupid gauges know who's BOSS!! In this thread we're gonna make a test box and then use it to determine the Ohms range for the sender we need. I would like to add that I did absolutely no research whatsoever so any facts may be hazy.

    Gauges will usually have three posts on the back. IGN GRD and SND. On all the good ones these are almost never marked. Typically, on the Stewart Warners that I am so fond of, If you are facing the back of the gauge the post on the right is IGN, the post on the left is SND, and the top center is GRD. The sender will be grounded and will have an ohm range it reports to the gauge. Ohms are the measure of resistance in a circuit and were discovered by Abraham Lincoln while flying kites in 1976.

    Things you will need:

    500 Ohm Potentiometer (NOT 500k)
    Something plastic to mount it on/in
    Alligator clips
    Soldering iron/solder
    Machine screws and nuts
    12v Battery

    So here we go

    Here's the Potentiometer. The center post is the variable one, the outers are hot.


    Mounting Box

    Battery 12v

    Find the setting on the multimeter that's just above the range of the pot. For this one it's 2000ohms. Hook up a lead to the center and to an outside and measure the resistance. This is to test the sucker. As you can see it's pretty much 0-500. Awesome. Time to move on.



    Solder some leads to the pot and hook em up to some screws making some sort of terminals. Drill the appropriate holes and mount that stuff in.


    Put a nice knob on it and hook all that shit up. You're gonna need to go from the IGN on the gauge to the + side of the Batt, from the SND on the gauge to a terminal on the box, from the GRD on the gauge to the - side of the Batt, and from the other terminal on the box to the - side of the Batt.

    Tested it out and it's workin!



    Here's a pic of it hooked up and a video of it working the gauge:


    So now that you're hooked up and you know it works here's the procedure. Turn the knob til the gauge is at it's highest range, for this Fuel Gauge it's at Full. Unhook the clips from the box and measure the Ohms- in this case it was 30 ohms. Now hook it back up and turn the knob up until it drops to it's lowest range (empty)-. Unhook the clips again and measure the box. For this gauge it was about 240 ohms. So now I know that this old Fuel gauge needs a sender that is 30-240 ohms and I can start hunting or modifying one to work. Now go build some shit!
  2. brokenspoke
    Joined: Jul 26, 2005
    Posts: 2,899


    Thats some pretty cool shit right there....
  3. Chris Casny
    Joined: Mar 13, 2006
    Posts: 4,870

    Chris Casny

    Awesome, very clever.
  4. 3wLarry
    Joined: Mar 11, 2005
    Posts: 12,804

    Member Emeritus
    from Owasso, Ok

    I'm lost with electrons...this is why I pay $1000 to have my cars wired. :)
    kidcampbell71 likes this.

  5. pinkynoegg
    Joined: Dec 11, 2011
    Posts: 1,135


    just what i needed!

    now to go fry some gauges, I mean see if they work....
  6. BuiltFerComfort
    Joined: Jan 24, 2007
    Posts: 1,620


    I found an old no-name temp gauge one time I liked - with this method I could have determined the gauge specs but I'd still need a sender to work with it.

    Does anyone have a list of commonly available sender units and their specs (and maybe where to buy them)?
  7. ... chainer... :D
  8. Simple and cool. Thanks.
  9. Now I can finally get the right sender for my trans temp gage. Thanks.
  10. rusty truck
    Joined: Dec 17, 2008
    Posts: 214

    rusty truck
    from rochester

  11. Dreddy,
    Where did you round up that potentiometer? Was that just one you had lying about or did you go to RadioShack or some other such place?
  12. Dreddybear
    Joined: Mar 31, 2007
    Posts: 5,982


    Ebay. 3 bucks. I bought it on my phone and it was in my mailbox two mornings later. The battery was 24$
  13. daddio211
    Joined: Aug 26, 2008
    Posts: 5,998


    No, this sounds about right. I actually laughed out loud at this.

    My '27 T Roadster build: 734383
    kidcampbell71 likes this.
  14. titus
    Joined: Dec 6, 2003
    Posts: 5,066


    Very cool idea, been meaning to do something like that for a while. cant you hook the multi meter on at the same time?

    Me and the old man were playing around with some 6 volt stewart warner fuel gauges and got the ohm ratings off an original send i had for one of the gauges and learned that vdo had a sender with the same ohm ratings but opposites, so i reversed the direction the sending unit arm came out if that makes sense.

    Cool Tech

  15. Kevinsrodshop
    Joined: Aug 22, 2009
    Posts: 590


    The only thing I can add is you are peforming these measurements using a 12 volt battery. When installed and being used in a car the voltage being used is 14.5 because the alternator (or generator for you traditional guys) is making power. Not a big difference in what the gauge will read but the only one that is really critical is the gas gauge at empty. If its really empty you want to know that.

    All boils down to Ohm's law's_law

    I did a thread similar to this but used an early 70s Ford cluster as the donor and it has its own voltage regulator to eliminate the variation of power supply voltage.

    But the theory laid out by Dreddybear is solid.
  16. 325w
    Joined: Feb 18, 2008
    Posts: 5,440


    Was that Abe are Ben that flew the kite.??????? Using the potentiometer you can dial the temp gauge to read where you want it and add resistors inline to keep it where you want it.
  17. Dreddybear
    Joined: Mar 31, 2007
    Posts: 5,982


    In case anybody was wondering I was able to order the correct senders and they work great!
  18. pinkynoegg
    Joined: Dec 11, 2011
    Posts: 1,135


    just waiting on my potentiometer to come in so i can start playing around with it. by far one of the most useful tech threads i have seen in a while
  19. joeycarpunk
    Joined: Jun 21, 2004
    Posts: 4,445

    from MN,USA

    Great useable tech, anybody else set something up yet?
  20. thanks i've just built one, was able to check out some old smiths guages i had lying around that were going to be wall hangers. Now they're in the box of parts for my next build.
  21. fordcragar
    Joined: Dec 28, 2005
    Posts: 3,180

    from Yakima WA.

    Great tech article, thanks for posting.
  22. AHotRod
    Joined: Jul 27, 2001
    Posts: 11,130


    Just what we all need in our shop, Thanks for sharing this, Great job!
  23. Dreddybear
    Joined: Mar 31, 2007
    Posts: 5,982


    Believe it or not the sender for my fuel gauge was the cheapo standard speedway one!

    Attached Files:

    • $_3.jpg
      File size:
      12.7 KB
  24. Cool
    I built one and tested my SW oil and water gauge and I came up with 8-360 and 10-425 sending units needed.
    Thanks for the tech.
    Where is the best place to locate sending units?
    Last edited: Apr 21, 2014
  25. Dreddybear
    Joined: Mar 31, 2007
    Posts: 5,982


    So Far I have managed to find all my senders on ebay..
    Joined: Feb 22, 2006
    Posts: 716


    Radio shack sells potenmeters, that's where I bought min last year.
  27. flatheadpete
    Joined: Oct 29, 2003
    Posts: 10,030

    from Burton, MI

    I prefer to locate mine on the car that needs them.....;)
  28. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,906

    need louvers ?


    Seriously Dreddy, this is frickin' brilliant! I have been straining my pea sized brain trying to figure out something similar forever, but never taken the time to make it happen. Good to see that it works, and that your analytical mind has made things much simpler than my Rube Goldberg contraption would have been....
  29. wex65
    Joined: Dec 19, 2012
    Posts: 1,100

    from WV

    Brilliant idea. Will use this to test out the 53 DeSoto gauges sitting on my shelf.
  30. 1oldtimer
    Joined: Aug 21, 2003
    Posts: 7,742


    They work great, I built a few from spare car parts over the years (didn't put them in a case though). But they all broke (funny how shutting a door on one will do that). I found a gauge tester on Ebay a few years back for $20 and it's in a metal case.

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