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Changing Speed/Tachometers

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  • Changing Speed/Tachometers

    After seeing some of the DIY glow gauge ideas posted, I've be thinking, since I'm gonna have the dash and gauge cluster apart, how easy(hard?) would it be to take gauges from another car and using them in mine??

    I'm talking about the mechanics of it, not the cosmetics. I can fabricate a new gauge cluster if this works out.
    I'm not 100% sure on how tach and speedometers work, so maybe this idea isn't even gonna get off the ground. I've searched through this, and several other boards, but I havn't gotten any solid information.

    Could someone shed some light on this issue??

  • #2
    Not sure about the speedometer, but the tach should not be too bad. A tachometer is derived from just the electrical difference between ground and the alternator. Two wires only, and they're fairly easy to set up.

    Speedo goes through the ecu I think, so I can't be much help here. Someone correct me if I'm wrong, though.
    "Is Wayne Brady gonna have to choke a [email protected]$#*??!!"


    • #3
      I know with my car (tachless) I can simply swap guages with another car that has a tach. Not sure if that would work on yours though.


      • #4
        What year/make/model car are we talking about? Most newer cars get their info from the computer which would make doing that VERY hard.. Older cars use a cable from the tranny to the speedo.. Thats just a matter of getting the right gear to match your speed..


        • #5
          Hello all -

          Like the person who started this post, I've been puzzled over this particular problem as well. I'd like to have my carputer (which at the moment exists only in my notes and on paper) track various levels of various bits of my car - a '62 VW Beetle with a baja kit. One of the primary reasons I'm interested is because my car doesn't have a tachometer at all .. just a speedometer, gas gauge, two lights (one for oil and one for the alternator/generator) and an odometer (to just 10k without the .1 mile), and that's it... and when the car was made 43 years ago the gas gauge was a brand new feature.
          And of course, not just no tach - no gauges for oil pressure, oil and brake fluid levels, oil and cylinder head temps (important in an air-cooled car that's playing in sand dunes), voltometer, RPM (tachometer) or a compass (though eventually I suppose GPS will handle that).
          These have various purposes - some of them would alert me to leaks and other problems. Some of them could be used for measuring my car's performance (don't snicker, Bugs can be hot-rodded too, plus mine can go places 4x4s fear to tread) or trip information or what her gas mileage is or whatever.
          So ... the questions arise:
          How does one get mechanical, analog data to become digital data that a program can understand, catalog, and use? There is fairly assuredly no USB gas gauge.
          What program is there (if any) that will use the data in meaningful ways (as described) and display it on my niffy 7" screen?

          I think that's all that's needed to know about the problem. If this has been covered, apparently I'm not creative enough with my search terms.

          If you want a picture of the car, there's one at my homepage, but keep in mind this website's still very much non-functional till I get a lot of things together:
          You are all guilty of feeding the drug habit I have: obsessing with my car. Damn you!!


          • #6

            What about using an LCD in place of the gauges?
            CarPC install is starting to come along again...


            • #7
              First, I don't want to completely destroy my original stock dash ... the LCD is going to come out of it instead.

              Second, OBD-II is spanktastic for vehicles about a third of my car's age but that doesn't really answer the questions I had about getting a spinning speedometer cable to read on my computer.
              You are all guilty of feeding the drug habit I have: obsessing with my car. Damn you!!


              • #8
                i wanna do the same thing i want to move my 4 guages (oil temp water temp fuel and voltage) to the front of my passenger side facing the driver and put a huge tach with shift light on the top left and have my speedo in the middle... then install 2 2 inch screens on the sides for cameras but i dont know how to hook up the guages :-(

                1994 ford explorer xlt v6 4L if that helps lol


                • #9
                  There are tach sending units for ignitions without a tach signal wire. You'll find them commonly used on late 90s Mustangs and other Ford products. Cost is about $100 and they'll interface to any aftermarket tach.
                  2005 Subaru Legacy GT
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                  • #10
                    Kinda missing the point here, guys...

                    An aftermarket tach ... won't interact with a computer. How do I get the computer to display my tach/oil/speed/mileage/etc?

                    I imagine it works like this:
                    1. Mechanical component is doing its thing (i.e., a spinning tire)
                    2. Another mechanical component measures (i.e., speedo cable spinning)
                    3. SOME DEVICE I WANNA KNOW ABOUT THAT ADAPTS #2 to #4, being...
                    4. My super awesome computer that shows me my speed
                    >>> normal wire/cable >>> some sort of adapter >>> computer. I'm interested in the adapter
                    You are all guilty of feeding the drug habit I have: obsessing with my car. Damn you!!


                    • #11
                      If you have ABS and electronic gauges, the spedo signals may originate from four ABS sensors, and then the signals travel through the car's computer; the car's computer then probably sends a PWM signal to the gauges for needle deflection.

                      Can you swap?? ..probably not unless it is an older car with mechanical gauges, but there is a way to do anything if you are motivated.


                      • #12
                        This thread basically goes over what's going on in another thread and I took the time to sort of merge the information I've found over there.

                        You are all guilty of feeding the drug habit I have: obsessing with my car. Damn you!!