Tilt/Trim Help Needed

[MSUFisherBear]

Hey all...

Long time, no post (sadly... no recent fishing to be posting about). I've ran in to a maddening problem that I can't seem to figure out.

Here's the deal... my Xpress has a 2016 Mercury 90hp 4 stroke on it. I'm having an issue where the tilt/trim is kicking on by itself and trimming the motor up. Luckily,  I think I caught it fairly quickly (at least the actuator hadn't went up in a cloud of smoke). Today, I decided I was going to dig in to this some. I unplugged the tilt/trim switch at the front of the boat and left unplugged. Hooked up the battery and nothing, or so I thought. About an hour later the thing kicks on again. This time I check the switch on the motor itself. Doesn't seem to have any condensation issues that I can visibly see, but I couldn't figure out how to actually unplug the switch (still looking for diagrams now; was a little nervous to screw something up). I also decided to take a look at the switch on the throttle. It seemed like it may be sticking a bit so I thought I might try cleaning it up. But, for the love of all things good, I can't figure out how to access the switch itself to clean and check the connections (short of taking the whole throttle control assembly apart). Here's an idea of what it looks like: https://www.vevor.com/products/vevor-side-mount-remote-control-box-881170a15-mercury-console-premium-8-pi?gclid=Cj0KCQiA3-yQBhD3ARIsAHuHT67QSTaP4sAHRSRamJ7pCPnSWXq3eT_x29gEhqK7iPPnCKcfVWPPOaAaAhyFEALw_wcB.

So... spray the rocker switch on the throttle down with some QD electrical cleaner. Hook up the battery. For about an hour, all is well. Then... the blasted thing goes fill trim in (completely opposite of EVERY time I've had the issue so far). That makes me think that the issue is at that spot.

So asking those with far more marine knowledge than I a few (probably dumb) questions:

• What's more likely? The issue is at the switch/rocker in the throttle assembly, the motor, or the relays?
• If in the throttle assembly, is there some magic way to access the switch/rocker? Is there a better way of cleaning this up?
• Any other places on these that I should be checking?

Sorry - still pretty new to the boating game, especially beyond the basic maintenance topics.

Thanks in advance!

[fishinwrench]

The throttle mounted trim switch on Mercs has been a POS forever (their R&D guys just have never seen fit to improve on it).   Moisture inside the switch is typically the culprit, but it might be the 3-wire harness that is built into the switch. (Red/Green/Blue). 

Disconnect your cranking battery until you can have it serviced.....or it will burn up your trim motor, turning a 300.00 repair into a 676.00 repair.   

[MSUFisherBear]

Thanks, Wrench!

I had that suspicion and was 99.99% sure that was the next move. I had done a lot of reading on that last night that kind of alluded to the same (but some said a "sticky" rocker could cause it, thus the QD move). I could only find a few, somewhat shoddy details on other forums with deconstruct for actually checking the switch/connections (which is the part that scares the bejeezus out of me being that it's at the throttle control). Making an appointment asap to get it back in and hopefully get it resolved. 

Another question... can these draw moisture even when covered? I almost always have the boat covered except when in use. For future reference, should I be doing something else to help?

Thanks for answering all the questions!

[fishinwrench]

3 hours ago, MSUFisherBear said:

Another question... can these draw moisture even when covered? I almost always have the boat covered except when in use. For future reference, should I be doing something else to help?

They SHOULDN'T.  Not any more than any other rocker switch on the boat......but somehow they seem to.     The tolerances (gap between the actuator bar and contacts inside the switch) are just too tight.   A tiny little droplet of condensation is all it takes. 

[yowoodchuck]

Thanks to you both, a boat I fish on has the same problem...merc throttle control, only in the summer in high humidity.  I will see if I can get a new switch.

[MSUFisherBear]

OK. Well - makes me at least feel better about what may have caused it. Thanks for the details on this one!

[MrGiggles]

You can unplug the control harness under the cowl to isolate it. Big round twist lock connector on the right side. If it still acts up the issue has to be in the trim switch under the cowl or in the harness. 

I have that exact control box on mine, if that's what you have too, I'd almost bet the problem is in there because it's a Chinese POS. 

[MSUFisherBear]

Yep. That one in the link is a dead ringer for the one on the boat currently. I'm still basically set on that being the problem child. I plan on trying to get the switch at the cowl unplugged tomorrow if I can make it home with some daylight to spare (just to see if I can coax the crazy thing to do it one more time while I'm there). But like I said, I'm almost dead positive it's in that throttle control. 

I guess I did have one other question for @fishinwrench... Is it pretty much a dead set point that I need to replace the switch at this point? Or can this be resolved with disassembly, cleaning and reassembly? I sent an email to Mercury but their response was, we'll say, slightly south of helpful. Not sure what I should be asking for/looking for once I get it in. I've seen a little of both in trying to research this issue.

Again, lots of thanks to the sage advice on this board.

[fishinwrench]

17 minutes ago, MSUFisherBear said:

 

I guess I did have one other question for @fishinwrench... Is it pretty much a dead set point that I need to replace the switch at this point? Or can this be resolved with disassembly, cleaning and reassembly?

You can overhaul the switch if you want, but I don't. 

I want it to be Mercury's fault when it fails AGAIN.   Not mine.    

This is a perfect example of how the Japanese engineers are better with electric things than the American engineers are.     Many Jap motors are wired so that the key switch has to be ON before there's any power to the trim switch.   

  Ahh, See.....they were thinking !   💡

[MSUFisherBear]

Duly noted. That's the way I was leaning, too, but wanted to be sure. Thanks again!