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  1. #1
    Join Date
    Feb 2017

    Default How to remove the MDC-1600 and replace with standard gauges

    The MDC-1600 is installed on most of the Moomba/Supra’s from 99 to the mid 2000’s.

    Steps to replace (each picture has four figures due to forum restrictions). PM me a request for the full PDF document with proper layout.

    1. Instead of removing the negative cable from the battery, I unplugged the MDC harness from the main circuit board which effectively cuts power to the unit. If you are doing any other electrical work, it is recommended to unplug the negative cable from your battery. (Figure 1)
    2. The MDC-1600 on the 2000 Outback is in the transom locker. Open your transom locker storage area and remove the two screws at the bottom of the back panel. Remove the panel to reveal the MDC-1600. (Figure 2)
    3. Remove both plugs from the unit and cut them off. I left about 6┬” of wire on the plugs in case I had to reverse course. (Figure 3)
    4. Found out there was a good bit of extra cabling which needed to be untethered from the main run from the cockpit. Carefully cut the zip ties and free the gray cable so it can be pulled up to the cockpit. (Figure 4)
    5. Move to the passenger area and continue to make sure you can pull the gray cable towards the front. I was able to pull it from the transom locker storage and left the excess in the passenger area so I could keep pulling it up to the cockpit.
    6. Once you get the gray cable pulled up through to the cockpit, you will need to remove the zip ties from the back of the console so the cable and main gauge wiring harness can be pulled out. These are screwed to the back of the fiberglass supporting the plastic dash panel. (Figure 6)
    7. There are two plugs on which need to be unplugged from the gray cable behind the dash. These are providing the speedometer adjustment and gauge power/data back from the MDC unit and will no longer be needed. (Figure 7a and Figure 7b)
    8. Carefully pull the gray cable and panel connector you unplugged in step 1 out of the mess of wires and take out of the boat completely. You will build the new wire harness using this cable.
    9. There is a blue wire plugged into the main switch panel circuit board just above the wiring harness labeled ┬“To Main Harness┬” carefully unplug the blue spade connector from the main panel circuit board. This is the positive wire of the current harness for illumination of the gauges and will be reused for the new harness. (Figure 9)
    10. Unplug all gauges and continue removing all wires attached to the gauge harness behind the dash. This wiring harness contains pre-wired multipoint wires for power, ground, and the blue wire for the gauge illumination. We┬’ll need to remove the yellow (data) wire from this harness later as this one is no longer needed.
    11. Remove the wire loom and all electrical tape from the gauge harness. The goal is to keep the power, ground, and blue illumination wire so we can reuse the harness. Here┬’s the harness with the wire loom and electrical tape removed (Figure 11).
    12. Remove the wires which won┬’t be used in the new harness. The two connectors on the bottom of Figure 12 were the power and data from the MDC to the speedo calibration switches. We┬’ll be using only the red and black wires from one of these sets and capping the unused black and red wires. Cut off all the connectors. (Figure 12)
    13. Choose one of the Red and one of the Black wires to use supplying power from panel to the gauges and cut the other two leads. Cap the ends of the unused black and red leads so they don┬’t short out.
    14. Remove the yellow wire from the harness by pulling the yellow wire out of the zip tie┬’s one by one for all 7 sets. Once you get all the yellow wires removed, you can pull the entire yellow out and discard that set of yellow wire. (Figure 14 Top Right) The cap to the blue illumination came off during the dismantling so I re-taped this using harness tape (NOT ELECTRICAL TAPE). (Figure 14 lower center)
    15. I decided to only use one speedometer, so I capped off one of the seven legs (currently only Black, Red, and Blue) of the harness and will just leave it in case I ever decide to add another gauge.
    16. At this point I┬’ve also cut the gray cable about 5-6 feet from the connector end, and now we need to remove the sheathing. Using a utility knife, remove the sheathing. BE CAREFUL! We need most of the wires in this harness as they contain all the sensor, power (both battery and ignition), and ground. (Figure 16)
    17. Once the sheathing is removed, we need to remove the connector and the wires which came FROM the MDC and going to the speedo calibration. (Figure 17)
    18. Cut the sheathing which remains holding this connector to the harness and unwind the wires out of the harness without bending or crimping the wires which remain. (Figure 18a) These wires will not be used and you can discard this connector and the wires which are connected to it. (Figure 18b)
    19. Using a heat shrink butt connector, splice the black wire from the panel harness to the black wire lead from the gauge harness, splice the lavender/purple wire from the panel harness to the red wire lead on the gauge harness. This is the ignition power source. (Figure 19)
    20. Extend the blue wire down to the where it runs just above the panel connector. I put a loop and zip tied the rest of the wires to the point on the harness where all the wires come out from the multi-leads on the gauge harness so the sensor wires can be routed to the appropriate gauge wire set. Make sure the blue wire is routed to just above connector on the gauge harness as it will be routed outside of the wire loom to be plugged back into the panel.
    21. The connectors I used needed to be stripped of sheathing. I turned the harness around after getting the connectors stripped and prepared. Start routing the sensor wires to the individual gauge leads based on the table below so that the sensor wire is even with ends of the blue, black, and red wires. (Figure 21)
      Color Sender Input
      Red Battery 12 vdc
      Purple Ignition switched 12 vdc
      Tan Temperature 80deg = 500 240deg = 30
      Light Blue Oil Pressure 0 psi = 240 80 psi = 33
      Pink Fuel E = 240 F = 33
      Electronic e = 0 vdc F = 2 vdc
      Black Ground
      Gray Tach 0 to 400 HZ
    22. I used the yellow wire on my connectors to match up with the sensor wire for the appropriate gauge. Extend the sensor wire so that it┬’s even with the other gauge leads and cut them at the same length so you can connect all the wire leads using heat shrink butt connectors. The RED wire from the panel harness is constant 12v which needs to go to the GPS Speedometer so I slipped some yellow heat shrink tubing over this wire to indicate it is the constant power to run to the gauge. IF you are using two GPS speedometers, you┬’ll need to run this wire to two lead sets. Label the leads as you go, and it should look something like this when you┬’re done. (Figure 22)
    23. The volt gauge does not have a sensor connector, so I placed a section of heat shrink tubing over the end of the yellow lead, doubled the dangling portion over and tape the end down.
    24. Test the gauge harness by taking it to the boat and connecting all the gauges before installation. Plug the panel connector in only after connecting all the gauges and laying them on the deck of the boat. Start the boat and make sure you get correct readings. I had pre-wired the ring connectors and a spade connector to the illumination wire(blue) to the back side of the gauge leads and connected them in an attempt make the installation of the gauges easier. This allowed me to test the gauges easily by plugging the male and female sides of the lead connectors together, however, this proved to be a futile effort on the 2┬” gauges as they don┬’t have enough clearance to connect the wires to the back of the gauge and get the lock ring tight enough to secure the gauge in the dash. The 4┬” gauges work fine for this installation and I recommend pre-wiring for any 4┬” gauge. Don┬’t pre connect the 2┬” gauges. I added an extension wire for the illumination lead on the gauge side quick connector on all the gauges so the ┬╝ spade connector could be plugged in more easily. (Figure 24)
    25. After verifying the gauges work, you should install wire loom over the new harness to protect the wires from chaffing. I ended up using an old drain hose as my wire loom for the large section of the harness(White loom in picture), 3/8┬” inch for the gauge leads, and ┬Ż┬” loom for the longer lead between the large section and the panel connector. Make sure to route the illumination spade out of the loom before the end of the connector as it needs to be plugged back into the panel into the same location from which it was removed. (Figure 25)
    26. Installation is straight forward as you need to Install the gauge according to the correct location and then plug the lead ends together. After gauge installation of the gauges, plug the panel connector back into the main switch panel (don┬’t forget to plug the blue illumination wire back to the original installation location).
    Last edited by Dstoked13; 05-16-2020 at 12:42 PM.

  2. #2
    Join Date
    Feb 2017


    FYI, if this seems too daunting for your skillset, Ron Tanis sells wiring harness kits (gauges included) here: search for your boat and he probably has a kit for it. I'd contact him prior to ordering since he custom builds these. This guy is a wealth of knowledge and recommend you go watch his videos if you want to be educated about ski boats in general. Go check out his YouTube channel as well:

  3. #3
    Join Date
    Jun 2007
    Vancouver, WA


    Nice write up and interesting. I may have to bookmark this one in case mine ever crap out.
    My mind not only wanders, it sometimes leaves completely.

    2001 MobiusV - Loaded with Ballast, Exile, Blood, Sweat & Beers

  4. #4
    Join Date
    Feb 2017


    Thanks... it all started with the striations and cracking on my gauges, speedos not working, got one working, tried to find a replacement for the broken one, gave up...then the oil pressure gauge started messing up. The forum rules prevented me from sharing the full text of what I wanted to share, then I had to highly edit what i'd written to stay under the word limit. According to Ron Tanis, they will fail at some point. Just make sure you disconnect the pitot tubes from the MDC when you winterize to prevent water infiltration into the electronics.

  5. #5
    Join Date
    Mar 2003
    s.e. washington state


    I was fortunate my 98 never had issues except the Airguide speedometers that I found a pair on eBay. People need to understand that most of these boards cannot be found in 5-10 years so being innovative is important. Most of those who have or had older boats have gone through this at one time or another so fixes like this are important. Kudos.
    1998 Mobius
    310 HP PCM

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