2001 Mercury 90HP 2 Stroke Starter Solenoid Issue?

[kgosselin]

Ugh. Just dropped my boat off at the a local dealer/service center, who seemingly by default, gave me the old "we cant even look at it for two weeks." Boat ran great Friday and Saturday. On Sunday, however, after motoring to our fishing spot, I turned off the ignition switch but could still hear what I presumed to be the starter still spinning. So, to stop it, I disconnect the positive battery cable from the battery. However, now, when I reconnect the battery cable, the motor wants to fire up, even if the ignition is turned to off, and/or I've taken the key out.

I suspect starter solenoid or ignition but don't really want to let my boat sit at the dealer for two weeks if they're not even going to look at it. Is it a good gamble to buy a new solenoid for approx $30, and swap it out myself?

 

[Texasmark]

The copper ⅜" studs on the outside of the starter solenoid are connected together inside the unit by a spring loaded copper disc, all heavy duty to carry the 150 amps rated starting current for that engine (I had a 2002). After so many openings, and so many pits caused by the inductive arc when the contact is opened, they can and will weld themselves together. That sounds like what you have.

If you are electrically inclined, you can run a test and answer the question yourself.

1. Remove the large, high current cable from the solenoid to the starter at the output terminal of the solenoid.
2. Get your ear close to the solenoid and have someone turn the ignition key to the start position.
3. Listen for a click (sound) coming from the solenoid. If you hear one, the problem is something else as the internal solenoid coil sucked the copper disc down onto the studs like is supposed to happen......it wasn't glued to them via arc welding.
If you don't the contacts are welded shut and didn't separate (action of the internal release spring). Or you don't have power to the coil in the solenoid or it's open circuited, in either case it can't pull the copper disc down and onto the studs. However, your problem is continuous current to the starter (keeping it spinning when it shouldn't be) and that's a stuck contact sort of problem, not solenoid activation circuitry.
4. The other possibility is that the ignition switch is shorted. However, a quick test of that is to pull one of the small wires off the solenoid and see if the starter still gets power with no energizing circuit hooked up. If so, again, welded contacts.
5. If you have a multimeter you can make a continuity of the studs with the power off, and measure voltages and all to support the above statements.

Betcha I boats sells them...top of the page under Boat parts and accessories.

 

[kgosselin]

Thank you Texasmark!
I've now confirmed that the solenoid contacts are in fact welded together. Mercury online parts catalog indicates the correct replacement is p/n 817109A2. I can order online but my local mercury dealer has 817109A3 in stock and says its the same solenoid but couldn't explain the difference between the A2 versus the A3 version. Any thoughts?

 

[Texasmark]

Basically you have wiring and mounting variations. You need the high current circuit so that's a no brainer. Most use ⅜" studs and that's adequate to handle the starting current for anything we normal folks would ever encounter 10 times over, so switching current rating is for the most part a no brainer. Also you need the coil that pulls the plunger down engaging the copper disc to complete the high current circuit so that's a no brainer.

On outboard engines, you usually have 2 wires for the coil, the small terminals, one in (+ from the start position of the ignition switch and one out -), with no connection to the case. That way you can mount the case to any surface you choose. If you bought a relay with only one small wire, the other end of the coil is tied internally to the case and relies on the mounting of the solenoid to a metallic surface in contact with the battery neg, or you have to add a tag wire under the mounting screw that goes to the battery ground which in OB engines is usually the engine block.

If you bought a generic 4 pin and it didn't energize properly, just swap the small wires to reverse the current through the coil. Some don't care about the polarity as the steel plunger is magnetically generic and will respond properly to either direction of current flow.

If you are a curious type, like I usually am, pop the top off the old one and have a look see at what happened. The little peaks and valleys you see reduces the surface area to the point where there isn't enough of it to remain cool during the 150 amp. give or take starting current and just like any metal welder, the heat melts the surfaces together.

 

[kgosselin]

Thanks again. Hoping to have the Mercury recommended solenoid (p/n 817109A2) later today. If not, I'll try the alternate 817109A3. Either way, I'll be on the water this weekend, even if I have to pull start the darn thing.