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  1. #1

    Default Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    Hi All,
    I have a Mercury 50 hp, 4 cyl, 1984 model. I had the carbs rebuilt, stator and trigger replaced in July. The compression is good the fuel line bulb pumps up hard and I know it is getting fuel. It ran well all summer and I put 60to 80 hours on the motor if not more. On occasion this summer when running the motor, the motor would cut off briefly then continue running. This would happen at WOT or half throttle or anywhere in between. Some days it would run flawlessly for hours then the next day it would cut out, but it would always refire and I would continue with my day. This weekend I winterized the motor and wanted to start it so I could fog the engine. After many attempts at starting the motor it would not even fire. I believe that it is an electrical problem causing this and that my previous stall outs are related. My theory is the "SwitchBox" is the most likely culprit. I would like to hear some opinions from anyone out there regarding this issue.
    Thanks for your opinions on this.

    Dave

  2. #2
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    9,768

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    Will spark jump a gap of 7/16" on all cylinders ????----------------------You can test the stator and trigger using an " ohmeter " as well .--------------Troubleshooting is the only way to go about this !!

  3. #3

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    The spark plugs are gap-less and the trigger and stator are both new this year. That is why I believe it is another electrical component causing my issue. What is the "Switch Box" function? Can anyone enlighten me that theory? Look forward to hearing from you.

    Dave

  4. #4
    Join Date
    Sep 2010
    Location
    ontario
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    9,768

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    Sorry, you need to get a spark checker ( adjustable ) and set the gap to 7/16" ------then check for spark.-------------------The switch box takes energy from charge coils and stores it in a capacitor.-----------Signals from the trigger unit release that stored charge to the correct coil via " switches " -------AKA silicon controlled rectifiers ---------- to fire the plug.------------Testing is the way to go !!!

  5. #5

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    Thanks racerone I agree with your approach. If I were to plug in a switchbox and it started up could I assume that the switchbox was causing my issue? I have access to one and want to try it. Any thoughts or issues on what I may encounter? Thanks,

    Dave

  6. #6
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
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    12,598

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    Could be the switch box, stator or trigger coil. The last two can be checked with a meter.

    First, get some old plugs and open the gap wide as possible, then do the spark test described above for all four cylinders.

    Jeff

  7. #7

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    Thanks for the info. I am going to pull it out of the garage and do these checks. Will let you all know what I find.

    One other thought that I had is that it could be a faulty ignition switch, is that something I should ohm out as well?

    Dave

  8. #8
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
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    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    Yes, but the easiest way to eliminate the switch is to disconnect the black/ yellow tracer 'kill' wire at the switch box and see if the problem goes away.

    Jeff

  9. #9

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    I am going to look at the motor running issues today if I get the time. Will keep you all updated.
    Thanks,

    Dave

  10. #10

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    Hi Y'all

    New to the Boating world
    My Friend has what I believe is a 1984 50 HP Mercury 4 Cly {I am a Auto Enthusiast} So I Rigged up this boat (all the old wires were shot) Except the keyed umbilical cord ) & we took it out yesterday & it was hard starting then after it got busted off It went maybe a mile & shut off . I mean to tell you no warning ,right here, right now, so we trolled a bit & then it started again & shut off again.

    I do not know all the parts of what makes a outboard work & I hope you all will help me get started like what is a stator & all the other stuffs

    Thanks a lot

    Slowride66

  11. #11
    Join Date
    Sep 2010
    Location
    ontario
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    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    Slowride, did it shut off like the key was turned off ???----------------Did it die out slowly and sputter ???--------Was it hard to turn over when it stopped???----------------Was water pump looked at / replaced ??-----------------------The more information you post , the easier it is to get good answers !!!

  12. #12

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    Hi & Thanks
    It Died like a switch & now on land we can't get it started & no spark

    We have not replaced the H2O pump yet we had to clean out the pisser tube but its pumping fine like to get it running before the water pump.
    It cad been sitting for a while

    It turns over just fine just no run.

    SR66

  13. #13
    Join Date
    Sep 2006
    Location
    Baton rouge, La, USA
    Posts
    1,702

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    is this the same problem that the thread was opened on?mercury for many years had lousy wires that the insulation went to hell and everything corroded and turned green...i owned two 4 cycle 50 motors and it happened to both of them...i dont know what year they corrected the problem....at one time there was an outfit in florida that sold those wiring harnesses....i have long since lost the contact but you may ask around to some old merc mechanics....

  14. #14

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    black stator with 1 red and 1 blue wire going to switch box + studed terminals = one side works rpm from start to 2250 or so then the other covers till WOT. as this may not apply a pm was sent. if it does I or davio will advise.

  15. #15

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    Wow! There is some interesting information written here. I pulled the boat out of the garage today. Before I installed the battery I went through all the Ohm checks on the coils, stator and trigger. They all checked out in spec as per the trouble shooting guide. I also went through and checked the wiring and connectors for obvious shorts, bad connections or damaged wiring. I also looked at the ignition switch wiring for issues. I found nothing obvious. I put it all back together and installed the battery. It fired right up after a single choke and ran like it should. Turned it of and on several times and ran it for 10 minutes or so and it never missed a beat. What could this issue be? While the engine was running I flexed and stressed the harness and other wires in the system. It still never missed a beat. Could it be a faulty ignition switch or main harness? Lets keep this dialogue going.
    Thanks,

    Dave

  16. #16
    Join Date
    Sep 2010
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    ontario
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    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    What do you mean when you say " started right up after a single choke "-----------------------------------Choke should be operated continuously while cranking the motor over !!

  17. #17

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    The Choke in "electric mode is only on when the key is pushed in & if you are doing it the old fashioned way "with the rope" the Manual Choke was only choked once .

    My Interpretation

    SR66

  18. #18
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
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    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    Considering the peanut butter-like insulation they used on the wires back then, I suspect you had a short to ground somewhere--and it WILL return.

    I replaced virtually every wire in one of those years ago--wire by wire--and you might have to as well.

    Jeff

  19. #19

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    I will address racerones' choke question first. I choke the motor when starting cold by pushing in the key while cranking, this activates the solenoid to pull the choke closed. This is what I meant by a single choke. I cranked it over, pushed in the key to choke it. I did this with 1/2 throttle as I always do when it is cold. It fired right up.

    With that said I have a question for fastjeff. Were the wires you replaced inside the engine cowling or in the external harness to the key switch? I have a harness available if I need it. Would that be a good approach to replace that? Or should I not bother with the harness and just focus on the engine compartment. Look forward to hearing back from anyone on this.

    This turned out to be an informative thread. Keep it going.
    Thanks,

    Dave

  20. #20
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
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    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    The rat's nest I had to change was inside the motor cowling. If yours is ratty, and you have a good one, by all means replace it--one wire at a time.

    Jeff

  21. #21
    Join Date
    Sep 2006
    Location
    Baton rouge, La, USA
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    1,702

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    agree with fastjeff on reworking the wiring(inside the cowling)....its a do it now or later deal on that....and later may mean a failure on the water...probably on a cold rainy day for a ground or short...been there and done that on THAT model and vintage motor...i still dont know if this thread is about the same motor that started the thread...i dont see where the spark has been checked for a 7/16 jump....this and letting it set and then restarting after it gets cold may show up an intermittent fairly solid...run the motor at night with no lights and the cowl off and look for a spark going to ground...look for melting under the stator...have an inductive timing light hooked up and around a plug wire while you are playing with this problem....i dont remember if a timing light will fire on the output of this stator or not....someone might jump in and answer that..to net it out i dont think the problem is fixed...you either run it away temporarily moving the wiring or something like the switch or stator is intermittent...good luck....

  22. #22
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    743

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    The 1984 has the copper harness and you rarely see harness damage unless melted. Check the rectifier as if bad it can make stator overheat and cause this problem. Also check the grounds to and on the coils and ignition mounting plate.

  23. Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    you may have a faulty tilt limit switch, disconnect black yellow wire located below rectifier.

  24. Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    you may have a faulty tilt limit switch, disconnect black yellow wire located below rectifier.

  25. #25

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    This is for Faztbullet. Explain in more detail how to check the grounds to the ignition mounting plate.

    This is for MIDNIGHTEXPRESS. I did not know there is a tilt limit switch. Explain that in more detail as where it is physically located and how to disconnect.

    Thanks for all your ideas here, I like the information, it gives me direction.

    Dave

  26. #26
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    743

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    Check the ignition plate (aluminum plate that switchbox mounts to) that it has all its grounds and they are tight and ground from coils are tight also.

  27. Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    from switch box top left between switch box and ign coils below rectfier follow black yellow wire to black round plastic mercury filled switch 3/8 nut ontop disconnect black yellow wire disconnect black yellow from switch box . tilt limit shorts ignition to ground so you dont damage water pump. cdi offers engine harness this web site should have

  28. #28

    Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    Looked at the TILT-LIMIT switch today. It is mounted toward the front of the motor above the rectifier. Removed from engine and did ohm check. It is open when upright and closed when tilted horizontal. I assume this is the way it is supposed to work so when the motor is tilted up it will ground out the line to frame. With that said could I remove this wire from the mercury switch and just take the switch out of the curcuit? Or do I also need to take the wire off the switch box as well? This switch would have to fail closed or have an internal short to ground to be defective. It may be. I did not fire up the motor today cause I need to pull it back out of the garage. Look forward to more input on this.
    Thanks,

    Dave

  29. Default Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    You can leave limit switch off black yellow needed for engine shut down however test ign whit kill wire disconnected.

  30. #30

    Unhappy Re: Mercury 50 hp, 4 cyl, 1984 Model, Switchbox Question

    I am going continue this conversation. I took the boat out the last 2 weekends and the motor ran perfect. Put it in the water today and it would not even fire. It is getting fuel. Put it back on the trailer and headed home. Very frustrating. Any theories out there other than use it for an anchor?

    Dave

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