Tach hookups

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    Tach hookups

    Found a cool looking old tach in a junk store and would like to test it. According to Google the tach is from a vintage mercruiser of some sort but no info on what post does what. The top hole is obviously the light. The top middle post and bottom two posts elude me though. Anyone have any ideas?

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    #2
    Alternator field tach?

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      #3
      Originally posted by not2hye View Post
      Alternator field tach?
      Could be. I came here because I have no idea. 😁
      Last edited by Rooney77; 06-20-2020, 06:21 PM.

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        #4
        I'll say
        A: 12v power
        B: signal
        C:ground

        Hey, don't lob factual statements at me as if they're insults

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          #5
          Originally posted by Rooney77 View Post

          Could be. I came here because I have no idea. 😁
          Diesel marine tachs use alternator field signal to signal rpm, people have used them to add tachs to first gen cummins pickups. Could be the A post.

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            #6
            https://www.fwmurphy.com/uploaded/do...00-02-0260.pdf

            Look at page 8

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              #7
              https://www.ebay.com/itm/Mercury-Mer...-/163498146861

              Check this out

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                #8
                https://forums.iboats.com/forum/engi...ry-tach-wiring

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                  #9
                  Gently scrubbed the back with some water. Not sure why there's a $ sign on it.

                  Attached Files

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                    #10
                    Originally posted by not2hye View Post
                    That's close but different connections. There is a 12v on the back of the tach so atleast its a 12volt tach. I hope to use it in the hot rod if it works.

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                      #11
                      Originally posted by Scott Cee aka 2drx4 View Post
                      I think I'm more confused now than I was. Boat folks have their own lingo. Weirdos.

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                        #12
                        Signal likely what comes from an GM HEI distributor.

                        The mfg looks like a Stewart Warner but usually they are really proud of their instruments even if they did move to mexico and would have their name emblazoned all across the front.

                        But seeing seeing the back its like their gauges.

                        What your calling a big S or $ stands for signal.

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                          #13
                          Originally posted by PAE View Post
                          Signal likely what comes from an GM HEI distributor.

                          The mfg looks like a Stewart Warner but usually they are really proud of their instruments even if they did move to mexico and would have their name emblazoned all across the front.

                          But seeing seeing the back its like their gauges.

                          What your calling a big S or $ stands for signal.
                          So you're saying the one insulated post is the signal wire?

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                            #14
                            Yes..Ill put an email in to my ex boss and ask his opinion if you like.

                            The large with insulator under it either goes to the negative side of coil or to HEI dist or field pole of alternator.

                            The other connections wont work if at least one of the power wires isnt insulated.

                            If the other two connectcons arent insulated and you put 12vdc to them they will short out.

                            Are B and C insulated and or do they have continuity with each other ?
                            Last edited by PAE; 06-20-2020, 07:16 PM.

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                              #15
                              Originally posted by PAE View Post

                              Are B and C insulated and or do they have continuity with each other ?
                              They don't appear to be insulated so I assume they have continuity through the housing. I'll have to check tomorrow.

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