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Only 10.5 Volts?

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  • Only 10.5 Volts?

    1990 351W, Tristar 190...

    With the engine running...
    If I check the voltage at the alternator, I've got 13.5V.
    And the non switched wires also show 13.5

    But the switched power (like the purple wire to the choke, or the pre-ballast purple wire) only shows 10.5 volts.
    Post ballast wire to coil is ~7.5V

    Is this normal? I expected to show closer to 12V on the purple wire.

  • #2
    ..........
    Last edited by Spork; 11-19-2015, 04:57 PM.
    /spĂ´rk/
    a spoon-shaped eating utensil with short tines at the tip

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    • #3
      Originally posted by hairlesshacker View Post
      1990 351W, Tristar 190...

      With the engine running...
      If I check the voltage at the alternator, I've got 13.5V.
      And the non switched wires also show 13.5

      But the switched power (like the purple wire to the choke, or the pre-ballast purple wire) only shows 10.5 volts.
      Post ballast wire to coil is ~7.5V

      Is this normal? I expected to show closer to 12V on the purple wire.
      Is the ground reference point the same for testing at the alternator and the purple wire? If you're using the ground under the dash as your reference for that test, measure the resistance from the dash to the battery - post, not the clamp. You'll see high resistance and if the ground buss is corroded, that's a good place to start.

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      • #4
        I was using the ground connection on the block (where the battery cable is bolted) as my ground for all tests.

        Messed with it more tonight, no engine running. 12.9 one orange side of the key became 12.7 on the purple side, but became 10.5 on the purple/switched wire on the bus on the back of the engine (which connects to the ballast resistor, choke, and alternator exciter)

        voltage at the hour meter looked ok, which seems to be about the only other thing on that circuit.


        I'm not sure I follow the comment about the ground...
        Maybe I'm chasing nothing here, but I'm not really concerned about voltage at the dash, I'm concerned that voltage to the coil/EI may be low causing an occasional weak spark/misfire.

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        • #5
          I have a 1990 Prostar and had same low voltage indication earlier this week I looked at connections. Behind the motor there is a square plug that carries about 7 or 8 wires to the instrument panel. I had corrosion on the connection. I pulled it and wire brushed the plug and sprayed WD 40 on it. Also there is another plug behind the instrument panel that plug looks the same as the one behind the engine. That one did not appear to have any corrosion but I cleaned it up also. Yesterday I ran the boat and Voltage shows 13 now on Gage where it used to show 11.

          Hope this helps. Gary

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          • #6
            Originally posted by Xjet2011 View Post
            I have a 1990 Prostar and had same low voltage indication earlier this week I looked at connections. Behind the motor there is a square plug that carries about 7 or 8 wires to the instrument panel. I had corrosion on the connection. I pulled it and wire brushed the plug and sprayed WD 40 on it. Also there is another plug behind the instrument panel that plug looks the same as the one behind the engine. That one did not appear to have any corrosion but I cleaned it up also. Yesterday I ran the boat and Voltage shows 13 now on Gage where it used to show 11.

            Hope this helps. Gary
            You may want to get some dielectric grease on those connections for longer lasting protection than WD-40 offers.
            Bailey
            '02 X-9
            Lake Blue Ridge

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            • #7
              CRC or Blueworks connection cleaner then dialectric grease to protect...
              sigpic...A bad day water skiing still beats a good day at work...1995 Pro Star 205....

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              • #8
                i had the same issue not totally sure what it was ,but i cleaned everything
                some info on my thread linked to below
                may help u with some troubleshooting may not

                the last thing i did that fixed it was to pull apart the black connector back by the motor tranny and put it back together


                HERE => ,,,,,http://www.mastercraft.com/teamtalk/...ad.php?t=58158


                ,,
                sigpic

                1988 mastercraft tristar (open bow).

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                • #9
                  Funny, the first thing I did was pull apart that black connector and clean it up.. Mine wasn't in bad shape though..

                  I didn't have the patience to go through all work you did to remove the dash, etc. That seems like a winter project. For now, I just grabbed a new wire soldered some spade connectors on the end, and ran it straight from the key switch back to the purple wires on the bus. It's not perfect, but it's not as bad as it was.

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                  • #10
                    none of my connections looked bad either .
                    i scratched my head for a few months trying to figure it out .
                    finally i just pulled it all apart . which i also think i didn't need too , i did clean up the wires, there where a few cut ones and new ones added but in the end the dash i don't think was the problem
                    i was about to give up and do what u did but i was going to run it from the switch straight to the coil .same thing .to the purple wire but it seemed to have sorted itself out once i pulled that rear plug apart . .

                    ...
                    sigpic

                    1988 mastercraft tristar (open bow).

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                    • #11
                      I had a similar problem with mystery voltage drops on various circuits. Like others, I pulled apart all the connectors and used a contact cleaner (DeOxit) on all the pins/sockets, then put them all back together. It solved about 90% of my issues.

                      If you want to track it down, take your VOM and start following wires from connector to connector and find out where the biggest voltage drop is. Take JimN's advice and keep the negative side of your meter connected to one location like the battery post; this is where a battery with both top posts and side posts comes in handy. The battery post is better than the block ground, because using the block ground won't find issues with the negative battery cable. Use the positive lead to check voltage on your purple wire all the way from the key to where you've found a low voltage.

                      /frank
                      1998 Maristar 200VRS

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