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  1. Member lpugh's Avatar
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    #41
    Starboard side of motor behind plenum very close to where the pressure line for the oil tank is connected, A lot of wires and oil lines in that area, just little to the left of where the 7 oil lines connect to the oil pump
    Thank You Leon Pugh

  2. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #42
    +1... Good idea to remove and clean that lug, make sure the surface of the block is clean, then properly reattach.

    I strongly suspect that either the SLAVE solenoid is intermittently failing, OR there is a keyswitch/harness problem. Really would be good if you could get a transom-mounted keyswitch harness to plug directly into the engine the next time it fails to start (which quickly tells the problem is inside the cowling our outside the cowling, with the exception of the battery/cables).

    Measure voltage at the SMALL yellow w/red stripe wire terminal on the STARTER solenoid when it fails to start. If voltage is below 10V here, check the voltage at both terminals on the SLAVE solenoid (large terminals).

    One other note: We commonly see positive cable connection post problems. The stacking order is specific and important- and the locking washer can sometimes end up with the "split" facing UP (allowing a bunch of liquid electrical tape goop to end up in the connections). Makes for some crazy intermittent problems.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
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  3. Member
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    #43
    Quote Originally Posted by EuropeanAM View Post

    One other note: We commonly see positive cable connection post problems. The stacking order is specific and important- and the locking washer can sometimes end up with the "split" facing UP (allowing a bunch of liquid electrical tape goop to end up in the connections). Makes for some crazy intermittent problems.
    Can you elaborate on the stacking order of the Positive Cables? I assume you mean on the Slave Solenoid, where all the Positive Power Wires come together w/ the Positive Battery Cable?
    Is the positive battery cable supposed to connect direct to the Positve High Current Side of the Starter Solenoid.. because on this motor, the positive battery cable seems to connect to the "main power bus" on one of the lugs on the Slave Solenoid, and then there is a relatively large jumper that goes from that lug to the positive lug on the starter solenoid.

    I would think connecting the battery cable direct to the starter solenoid, and then letting that jumper go for the starter solenoid to the power bus of the slave solenoid would deliver better starting current to the starter.
    Last edited by MichaelJ3; 07-02-2020 at 04:11 PM.
    2016 Ranger 1850 LS Reata / Merc 150 4s / SmartCraft / Lowrance HDS Carbon SS3D

  4. Member lpugh's Avatar
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    #44
    Don may not get back for a while as he is really busy these days, I will repeat what he has said many times and agree with
    The main cables that go to the motor are the first ones installed on the the battery stud post then stack from largest to smallest being at the top, No wing nuts, Don seems to prefer nylocks, this is where I differ a little as I prefer quality plated Flange lock nut as I think the contact area is a little better. However Don is the guru on these motors and you will never go wrong following his advice, I am a auto tech with some Merc outboard experience
    There is one draw back with flange locks, if you tighten them to much they may not come loose in the future risking a broken battery post if it is a studded battery
    If a dual terminal battery (has studs and posts) use post adaptors that have a stud and connect the main battery cables for the motor to these and every thing else to the stand alone studs

    I have seen a few motors where the battery cable is ran to the power point and jumper cable from there to the starter solenoid, I feel this is not the best way.
    Should be, the main cable should go directly to the starter solenoid and jumped back to the power point, that's just my opinion and I'm sticking to it unless Don says otherwise
    Last edited by lpugh; 07-02-2020 at 04:40 PM.
    Thank You Leon Pugh

  5. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #45
    The Opti's (and most other later engines) have a "Power Post" or point where the battery cable joins to the various legs of the wiring harness. Just prior to the "Power Post" models the same thing was done on the SLAVE solenoid.

    In either case, there is a cable that jumps up to the starter solenoid post.

    While I can understand what Leon is saying- and from an Automotive Standpoint he's correct, this is quite different in Marine applications. We never know how many feet the keyswitch harness wiring will have to travel to bring the "switched ignition power" and "starter activation circuit" back into the cowling.

    A main power relay is required- and that relay cannot remain closed (closed contacts) if the voltage drops below 9.5 VDC (actually gets a bit sketchy below 10V). Due to the voltage drops that will be present on the afore-mentioned circuits, more emphasis has to be placed on clean/solid power for the PCM wake circuit and the MPR (without those circuits the spinning starter serves no purpose).

    I played with this idea back around 2008-2009 when we were having some cold-start, low-voltage problems on a specific engine. Moving the battery cable over to the starter actually made it worse (in some cases you couldn't even get the engine started due to low voltage for the wake circuit and MPR). That situation turned out to be totally different (PCM calibration glitch).


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
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  6. Member lpugh's Avatar
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    #46
    Thanks the explanation on why that was done, never quite made since to me, does now
    Glad to see you got a little break time to be on here
    Thank You Leon Pugh

  7. Member
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    #47
    Well, this particular motor is wired with battery cable to the 12V source side of the slave solenoid. However, the service manual has the below as a starter circuit wiring diagram. This is what got me asking the question in the first place. Now, I see that there is a newer P/N for the service manual than this one. The excerpt is from P/N 90-85945R1, Merc now shows a Service Manual P/N of 8M0057453, not sure if there was a design change or not.

    83421765-B720-4DF7-8320-1B8950686FA1.jpeg

    The battery has engine cables first, all other lugs next, largest to smallest. Lock Nuts on Posts.

    Was actually hoping this was just a wiring issue inside the cowling, with Battery Cable in wrong spot, now not so sure.

    Tomorrow FIL (father in law) will check GND lug, and was planning on moving the battery cable to the solenoid...but, now awaiting advice.

    P.S. Is there a correct stacking order for all the wires piled with the Battery Cable on the slave solenoid (engine end of battery cable) if that is indeed where the Positive battery cable goes? I was thinking it should be battery cable, jumper to starter, then the rest from largest to smallest.
    Last edited by MichaelJ3; 07-02-2020 at 07:00 PM. Reason: Added question about correct engine side stacking of cables.
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  8. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #48
    Diaphragm you posted is wrong.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
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  9. Member
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    #49
    Quote Originally Posted by EuropeanAM View Post
    Diaphragm you posted is wrong.
    OK, can you advise of the stacking order of the wires on the Slave Solenoid post, as that is where the positive battery cable connects to the engine.
    2016 Ranger 1850 LS Reata / Merc 150 4s / SmartCraft / Lowrance HDS Carbon SS3D

  10. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #50
    Just a note: Keep seeing a 150 4S in your signature... thrown me for a loop more than once.

    Pretty much the opposite of how you do your battery connections. I would recommend the Starter's large cable FIRST, the smaller lugs for the wiring harness, the Fusible link lead for the alternator, the LOCKWASHER with the split facing DOWN, the BATTERY power cable, and then the nut securely fastening all of these.

    Liquid electrical tape the entire connection once complete.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
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  11. Member
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    #51
    Quote Originally Posted by EuropeanAM View Post
    Just a note: Keep seeing a 150 4S in your signature... thrown me for a loop more than once
    Sorry, this thread is me communicating on behalf of my father in law, who has the 150 OptiMax w/ S/N listed in post 1 of this thread.

    Thanks for the advice on the stacking order. Will verify that.
    2016 Ranger 1850 LS Reata / Merc 150 4s / SmartCraft / Lowrance HDS Carbon SS3D

  12. Member
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    #52
    Quote Originally Posted by EuropeanAM View Post

    Pretty much the opposite of how you do your battery connections. I would recommend the Starter's large cable FIRST, the smaller lugs for the wiring harness, the Fusible link lead for the alternator, the LOCKWASHER with the split facing DOWN, the BATTERY power cable, and then the nut securely fastening all of these.

    Liquid electrical tape the entire connection once complete.
    Note, FIL tried 2 stacking strategies on the slave solenoid. First was main battery cable on the bottom, followed by jumper to starter, then remaining lugs from largest to smallest. Second was your recommended stacking.
    First method started every time (10x attempts)
    Second Method resulted in about 25% starting success.

    He was unable to locate the GND lug, and has given up. Hauling boat in to a Mercury Mechanic (Same one who replaced Slave Solenoid last year).
    He is considering asking them to replace the main battery cables and the key switch wiring harness, as these are the only elements of the starter circuit he has not replaced in the past 12 months.

    I suggested he ask them to load test the battery (in the unlikely event is is bad), and also to follow Don's suggestion of trying a transom mounted key switch harness connected directly to the motor to rule out any issues w/ the remote key switch harness, before replacing it for no reason.

    Hoping they are good at what they do, and get this figured out for him, he has an upcoming fishing trip and wants to have confidence in his rig again. I will post the diagnosis and repair when I know it. Thanks to everyone for trying to help.

    Note, we did try measuring some of the voltages during these start attempts, but it is difficult to do w/ a DC voltmeter, an oscilloscope or a datalogger would be better, as the reaction time of the voltmeter is too slow to really get a good reading.
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  13. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #53
    I've had pretty good results from using a carbon-pile or fixed resistor type Load Tester at various points (slave solenoid and block ground, starter solenoid and block ground, etc) to determine if indeed there are any amperage availability problems (while voltage drop tests are great, I actually prefer this method because it's a real-world LOAD between two points). If one cable is suspect you can bypass to the battery and confirm that is the case.

    Keyswitch Harness: Perhaps. Most dealers have a transom-mounted (portable) keyswitch harness that can be plugged directly into the engine for testing.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
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  14. Member
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    #54
    Father-in-law picked up boat today from dealer. Replaced Key Switch Harness, seems good now.
    2016 Ranger 1850 LS Reata / Merc 150 4s / SmartCraft / Lowrance HDS Carbon SS3D

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