Shift interrurter switch

Chris60Chris60 Member Posts: 12
I have a 1999 maxum 19sr with a 4.3 vortec mercruiser. Awhile back the problem I had was when I reached around 3k rpm it started to rattle and back fire through the throttle body. After checking into it I found that the OHMs going from the interrupter switch were breaking down. To double check I bypassed the switch with a jumper wire took it for a ride and it ran great. So I replaced the switch with a Sierra product. To it for another ride and it ran good no problems for a good while. Coming back into the dock it started having the same symptoms. My question is what would cause those switches to go bad that quick or what should I check? Everything is new coil, ECM, motor, risers and on and on. Could it be an adjustment ? 


  • PickleRickPickleRick Member Posts: 2,301 ✭✭✭
    The interrupt is just a simple normally open switch, 2 wires?  
  • Chris60Chris60 Member Posts: 12
    PickleRick I understand its an open and close switch . My question to you is what causes them to go bad. When pushing the button in manually it shuts motor off like it suppose to. The problem is the switch also sends that message to the brain as ohms and in turn if the ohms are spurratic at a high RPM it causes the motor to pop and rattle. Reason I know that when I disconnect the switch and put a jumper wire on the ECM side plug of the interrupter and put it in gear very slowly and throttle up it ran like a new boat. Only had 2 hrs. on the new switch when it started to pop and pin. 
  • PickleRickPickleRick Member Posts: 2,301 ✭✭✭
    edited February 10
    Have you verified with a multi meter the new switch has gone bad as a sticky/out of adjustment shift cable can cause this issue.

    The reason i asked is mine on my 93 rinker alpha 1 is a simple 2 wire so it's east to verify if the switch is falling via a multi meter.  If yours being for efi has more than 2 wires then id need to look more into it to see why its failed.
  • Chris60Chris60 Member Posts: 12
    Mine is also two wires. I have some time today to look into all that you suggested. I will get back to you on my find. Thanks!  
  • PickleRickPickleRick Member Posts: 2,301 ✭✭✭
    Ok, so if yours is wired like mine (n.o. or normally open) it  closes the circuit (connects the two wires) when switching gears so that it grounds the coil for just a split second to take the load off of the outdrive where you can change gears.  

    There shouldnt be current going through this to burn it up, think of it as an old go cart engine where you pushed a metal tab down on top of the spark plug to kill the engine, your kill switch just connects that ground.  

    Its easy to verify a normally open or normally closed circuit via a multi meter.  Put it on continuity test (beeps when leads touch)  a normally open switch wont beep until the button is pushed in, the normally closed wont stop beeping until its pushed in.

    Yours being efi(i nor my friends/family i work on have efi either)might operate differently but the adjustment procedure for the cables should remain the same.  In other words yours might not have a coil that it grounds out so verify if you're n.o. or n.c.  whichever you are verify its not activating when it's not supposed to be activating.  This may require a buddy when testing and just because it passes the test on land or even on ear muffs doesn't mean it will work in water as water puts a load on the outdrive which you cant replicate with muffs on land. 

    The shift cable doesn't have to stick too badly or be too far out of adjustment for it to act up and I've seen more than a few that worked fine when they just start the boat then act up once its been running a while. I assume once the engine bay warms up it makes the cable more stiff but I've never verify 100%.  Lubing a sticking cable seems to be a temporary fix at best.

    There is a good write up on iboats on the adjustment procedure and for those like me that hate reading but like a video how to, there are more than a few YouTube videos on the procedure.  

  • AlswaggAlswagg Member Posts: 2,800 ✭✭✭✭✭
    You need to adjust your shift cable 
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