1978 Mercury 200 20 hp, electric start

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  • September 13, 2020 at 8:24 pm #216363
    Buccaneer
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      US Member

      The subject motor came with a recent boat purchase. I decided to check it out before I sell
      it, hopefully as a running motor. I was told it ran a couple of years ago, but in looking at the
      wiring, I have my doubts.
      What the cause of of all the insulation disintegrating on Mercury’s wiring in that era?
      I decided to try to patch up the wiring before I even try to crank it over to check for spark
      or compression.

      I found one wiring diagram that’s “close”, but it’s not showing the rectifier that mine has.
      Wouldn’t they all need one in that era to charge the battery?
      There’s two wires from the stator going to the top of the rectifier, then one going to
      the positive 12 v from the battery.

      I pulled the flywheel and don’t see any bad wiring right at the stator, but the rest of the internal
      wiring harness was a mess!

      Anyone have a digital repair manual for this model?
      The serial number is in the 49XXXXX range.
      I’m used to working on the old magneto units!
      Thanks.

      Merc-200-Wiring-diagram

      DSCN9465

      DSCN9469

      DSCN9466

      Prepare to be boarded!

      September 14, 2020 at 5:45 am #216380
      billw
      Participant

        US Member

        Yeah, the electric starts had those rectifiers. That’s the right one. On the insulation, it really is a shame how it goes bad, because originally, it seemed like really good-quality, flexible wire.

        Long live American manufacturing!

        September 15, 2020 at 4:51 pm #216509
        Buccaneer
        Participant

          US Member

          Update – I patched all the wiring up on the internal harness….. pretty much replaced
          all but the large battery leads. Hooked up the external harness today to a battery,
          and the starter works, the motor spins over, with 116 psi on both cylinders,
          and it has spark……. at least on my conventional test plugs. I did not try
          the surface gap plugs that came with it.
          That’s a good start, and a surprise after seeing all that wire crumbling apart.
          I took the motor off the stand and threw it on the back of the boat, being the
          motor is a long shaft and too long for the stand it was on.
          Sometime yet this week I hope to hook the muffs up to it and see if it will run,
          if’n the carb isn’t gunked up.
          I need to check the lower unit yet. Do the 1978 Mercury’s use conventional marine
          80 / 90 weight gear oil?
          If it runs, what would be an average asking price for this MN Mercury?
          Thanks.

          Prepare to be boarded!

          September 15, 2020 at 8:27 pm #216526
          dave-bernard
          Participant

            US Member

            yes on the oil. don’t forget to replace the impeller.

            September 15, 2020 at 10:23 pm #216529
            Buccaneer
            Participant

              US Member

              Thanks Dave. Will see if it runs so I can sell it for more than parts, and if so,
              will put a new impeller in it so it’s “good to go” for the next owner.

              Prepare to be boarded!

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