Starter slave Solenoid
 

Who knows what the purpose of this solenoid. How can you tell if it gos bad. Why not just the starter solenoid.

Purpose? Start the boat:p
Boat wont start if it's bad!
Solenoids are generally used when the current exceeds the capability of the circuit, ie. the keyed ignition circuit. The ignition should be able to handle the current to activate the starter, but other devices like the neutral safety switches may not.
Just my guess.
Gary

Thanks Gary

I tried to figure that one out myself. I don't really understand the use of two start solenoids either.

When mine went out it would just "click" like the battery was dead. But with repeated attempts it would finally engage and crank the engine over.
Easy way to test is to jump the two large teminals together with a screwdriver or pliers. Use caution! This bypasses the solenoid and sends power directly to the starter. If it works that way and not with the key it's probably shot. I believe a new one from Merc is about 20-24 bucks.

thanks Iggy

Dont be confused between solenoids and relays.
relays allow you power large currents form a small
source. A solenoid will move something like engaging
the starter gear in to the flywheel then the relay in the starter will kick in and start turning the starter motor.

Scarab105 is right. The "starter slave solenoid" is a relay. The terms seem to be interchangable when it comes to starting circuit. Merc even calls the starter relay a "starter slave solenoid".
Oh well. I still stick to my guess. Anyone got any other ideas, other than to add one more part to fail?;)
Gary

The slave solenoid (relay) requires less amps
to operate than the starter solenoid.

With all the different sizes of boats out there,
and the different lenghts of wires used,
it's much easier to use a low amperage
relay, than to run heavier wire throughout
the starting circuit.


my.02

jt

You are right about the relay part of this but the solenoid part of this actually moves the starter gear forward to engage it into the flywheel.

Is it possible that it could be weak and not allow the starter to turn as fast as required or even make the battery appear to be dead or it just engages the starter solenoid and the battery takes over from there.

my understanding is that many times the small wiring to and from the helm creates such a voltage drop that the average starter solenoid made for auto applications will not fire without the slave relay that is designed to fire on lower voltage. Years ago on our old jet boat we had to run a ford solenoid to fire the gm solenoid because of the long wire run. We were told to use ford solenoids as the slave as they would fire on less voltage. Don't know if it was all true but it did work.

It been my experience that the stater assist relay willl die long before the starter solenoid. To test, simply use a volt meter. There should be only 4 leads: a ground, a solenoid line from the ignition switch (both small gauge) a 12 volt supply and a lead to the starter solenoid. Put the VM between ground and the solenoid line and turn the key to start: you should go from 0 to 12volts. Now verify that one of the big leads has 12 v when the key is on, then move the VM to the other big lead and turn the key to start; you should go from 0 to 12v. If not, the relay is bad. At least that how my Merc works.

JT's on the right track with the length of wire from helm to selenoid(relay).In your car the ignition switch is only 5-6 feet from the starter selenoid and battery.In a boat the power has to go from the batteries to the helm ignition switch then back to the motor.Thats about 40 feet of wire.It would have to be pretty heavy wire to engage the starter selenoid and even then voltage drop would be an issue.To test just jump it with a hot wire from the battery.The selenoid will have a hot wire,a trigger wire from ignition,and a wire to starter selenoid.If you jump the trigger wire and it cranks your problem is up river.If it doesn't crank but does when you jump the wire to stater then it's the selenoid(relay)If it still doesn't crank jump the selenoid right at the starter.If it cranks theres a problem in the wire from the relay selenoid to the starter selenoid.If it doesn't crank there is a problem with the starter selenoid,starter,or wiring to starter.You can here if the selenoid is engaging when you jump it.Don't be quck to pull the starter as the problem is most often wiring related.Dirty terminals,rotten wire end,bad battery swich,etc.I have been guilty of looking for a big problem when it has been as simple as a rotten wire end.I pulled a starter a year ago thinking it was bad because it would not crank on either battery and it turned out to be a bad ground wire.The grounds were common from the batteries but I just wasn't thinking out side the box till I stood on my head for 4 hours changing a stater.