'90 model Mercury 40hp pull start outboard. Forward controls "electrified"!!!

Discussion in 'Outboards' started by djaus, Mar 23, 2014.

  1. djaus
    Joined: Jun 2013
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    djaus Salted Nut!

    Firstly this motor doesn't use a battery.
    I have noticed recently that the forward controls have a current running through it. If I touch the controls & touch a metal fitting on the boat at the same time I get lit up!

    The controls consist of a standard forward/reverse lever & a run/stop switch. It is the switch that is funneling roughly 12 to 20? volts through the control body & then into me when I touch it & earth myself.

    What would be the issue? I'm thinking a bad earth maybe. The motor otherwise runs perfectly. I plan to clean the one earth point on the engine base (a bolt on the lower cowling) & then inspect the forward run/stop switch itself.

    I noticed the problem a week ago, while resting my hand on the controls I touched my leg on the metal part of the seat base (seat is screwed down to timber only). I felt a stinging sensation on the back of my lower leg & realized my leg was earthing the controls against the metal.
    20130816_151927 controls.jpg 20140119_171025 earth.jpg Red arrow indicates earth bolt
    20140119_171440.jpg
    Any suggestions for a cure would be great, thanks.
     
  2. CDK
    Joined: Aug 2007
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    CDK retired engineer

    The switch shorts the primary ignition pulses to stop the engine; the peak voltage is approx. 200 V.
    If the switch functions it means the ground wire is OK, there probably is moisture and some dirt in the control housing or a breach in the insulation causing part of the voltage to appear on the lever.
     
  3. djaus
    Joined: Jun 2013
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    djaus Salted Nut!

    I second guess myself when it comes to things of an electrical nature, but I kinda' figured it was something like that. Obviously it's not earthing properly & it would be one of the things you mentioned.
    A simple but ~~~*SHOCKING*~~~ problem
    I'll open up the controls & have a look.

    ummm...200v...CRIKEY!!!

    Thanks CDK
     
  4. djaus
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    djaus Salted Nut!

    Had a bit of a look today. Disassembled the forward controls & found a small crack in the insulated/siliconed section directly behind the switch, where the insulated wires go in/out. The connections on the back of the switch have been siliconed up & looks factory standard to me. Doesn't seem to be any damage to the insulation on any of the wires.
    Also cleaned the earth on the engine & the wire connectors (x3).
    Merc classic wiring diag.jpg Found this online too. Very handy.

    I can't disassemble the switch itself either, it "appears" to be all one piece.
    The alloy housing surrounding the toggle switch is on a threaded shaft but it doesn't wanna' come off, just kept spinning!

    The other thing I did was to use a volt meter on the controls/switch.
    I'm not very familiar with it but I set the DCV to "20", then connected a circuit between the controls & the steel seat base. Got a base reading of 0.30 & then up to 0.75 with the revs cranked up. Not registering any AMPS though.

    What does this mean exactly?
    Point 3 & .75 of a volt, would that sound right?
    Thing is when it buzzes my leg it feels like at least 12 or 24 volts but it could be 30v to 75v as per the volt meter test. I can't leave the back of my leg there for long 'eh, she starts to sting pretty good!

    The other thing I made a note of is instead of a neutral safety switch my controls have a 2 spade pin plug in the front of the controls housing. What is it's purpose?
     
  5. CDK
    Joined: Aug 2007
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    CDK retired engineer

    The readings on your volt meter don't mean anything. There are approx. 200 V narrow spikes on the live wire of the stop switch, you would need special equipment like an oscilloscope to see it. Check if the ground wire is firmly attached to the alloy housing, any voltage leakage should go to ground there instead of through your legs.
     
  6. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Such are the joys of old outboard motors. Fix one problem, and the next one won't be far behind it !
     
  7. djaus
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    djaus Salted Nut!

    "Touche"
     
  8. djaus
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    djaus Salted Nut!

    The earth screw & all 3 wires on the base of the alloy cowling have been cleaned & should be doing it's job. I think the crack in the insulated/siliconed part of the switch would be causing the problem.

    Could I just add another wire to run from the body of the controls back to the engine earth?
    Or perhaps run this wire to a metal fitting on the boat? (steel handle on the cab or seat base)
    This would solve the problem yes?
     
  9. djaus
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    djaus Salted Nut!

    QUOTE: The other thing I made a note of is instead of a neutral safety switch my controls have a 2 spade pin plug in the front of the controls housing. What is it's purpose?
     
  10. Dave T
    Joined: Sep 2011
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    Dave T Senior Member

    Usually the connection at the front of the control is for connecting a tachometer and has 3 terminals if so then the wires that go to this connector should be a white which is the 12V positive, a black that is 12V negative ground and a brown wire that is the sender wire for the tach that connects to the alternator. Since your motor is a pull start then it may not have an alternator. If it does then it's possible that the brown wire in the control is shorted to the case which would give you a shock when the motor was running and you touched the case of the control and you were also touching something that was grounded. Do you know if this is the control box that came with the motor when it was new?
     
  11. djaus
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    djaus Salted Nut!

    Dave T, there's no guarantee that the current controls are the original, I'd say they are though. Before I painted it, it had the "Mercontrol" label affixed.

    As for the wiring, I opened up the controls a couple days ago & I can confirm there is only 2 wires. 2 wires running from engine to switch, & 2 wires running from the switch to the blank plug. Only 2 spade connectors (the plug) & those 2 wires/plug are well insulated in rubber. I did say though as per previous post that the switch/wire connection part itself is cracked.

    I'm thinking I should just change out the switch with a new toggle switch. In theory this would solve the "power to ground" leak.

    ...& no, no alternator on my motor. Refer to the wiring diagram posted above.
     

  12. djaus
    Joined: Jun 2013
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    djaus Salted Nut!

    Fitted a new toggle switch today. Problem solved.
     
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