Mercury 150 black max trim question

[SkeeterDuke15]

so i went fishing last weekend and the motor/ trim worked great as it normally does. then all of a sudden 2 days in to the trip my buddy and i were cruising down the lake and my motor trimmed itself all the way up. obviously i noticed it, stopped the boat and killed the motor before the lower unit was exposed but it just kept raising until it maxed out. we couldn't lower it and it just kept trying to raise by itself..... im a novice at this stuff but i know a little bit of how the back of the boat is wired up, so i checked for loose connections or a short at the hydraulic pump and wiggled a few wires and was able to get the motor back down. i dont really think i did anything wiggling cables but thats what made it work. i have since been out of town for work and will hopefully look at it this evening throughout this weekend but i wanted to know if anyone has had a problem like this before. the boat is a 1994 Skeeter ss140, 1979 Black max 150, unknown hydraulic pump( for now i will get more info on it later).

Thanks. Nick

 

[alldodge]

Probably the trim switch on the throttle, they go bad and get stuck. Had to replace mine 2 seasons ago

Only other item is the up solenoid gets stuck

 

[Chris1956]

If you have the toggle style trim switch, they can get rainwater in them and it will complete the Up trim circuit.

 

[SkeeterDuke15]

update.. so i was running WOT for 5 min or so, had not touched the trim button for a few minutes and had the problem. as well as when we had stopped, i turned the key off and we fished for a few minutes and heard a clicking noise coming from a solenoid. then the motor raised up a few inches. that was it, didnt do it again. ive checked the wiring and cant find anything weird. so maybe a bad solenoid?

 

[alldodge]

so maybe a bad solenoid?

My first guess is the trim switch not the solenoid.

Trim the motor down some so its somewhere in the middle or full down. Now take the thumb toggle trim switch and barely move it up, then release. Do this a few times just a little and see if it gets to the point it goes up on its own.

 

[QBhoy]

99% the switch on the throttle...or engine, if fitted.

 

[Texasmark]

Probably the trim switch on the throttle, they go bad and get stuck. Had to replace mine 2 seasons ago

Only other item is the up solenoid gets stuck

+1.....

On the switch either mechanically breaks, or little slivers of silver migrate between the contacts till it makes a path for conduction and the switch is shorted.

On the relay, as time passes, any time you have a motor involved, a spark is generated when the current is interrupted...like every time you tap your trim button. That causes material on the points in the trim relay (separate circuit in the relay from what the trim switch controls) to make mountains and valleys as material migrates to the other contact. In time the surface area contacting is not great enough to support the required current and wala....you have an arc welder and they are welded shut.

With what you said and you were just humming along and not on the button when it happened, I'd go with both AllDodge and QBhoy on bad switch...the one you use the most, or exposed to the weather, aka as suggested, the one on the throttle/shift handle.....easily replaced.

 

[SkeeterDuke15]

ive checked the throttle and everything looked ok. however! the switch on the motor was corroded pretty bad and while we were messing with it we raised the motor up a little and the switch stuck. so for now ive disconnected the motor trim switch, will replace soon but as soon as the weather gets better ill get back on the water and see if i have the problem again. thanks for everyones suggestions!