I took my boat out fishing yesterday and washed everything down when I got home. I put the boat away and walked past my garage a few minutes later. I heard a strange noise in the garage and realized the trim motor was running. I have a 2005 Mercury 90hp 2-stroke. The motor was in the full-up position and as soon as I pushed the down switch (on the throttle handle) the trim quit running. I trimmed the motor back down, messed around with it for a few minutes, and couldn't get it to do it again. This morning it started doing it again. I trimmed the motor down, it would stay down a few minutes, and then start trimming up by itself. I finally had to disconnect the battery to get it to stop. The motor did this one other time last summer on a rainy day when it was parked outside, but I couldn't ever get it to do it again and forgot about it.
I'm gussing there's a short somewhere in the trim system. Anyone run into this before? Are there any known problems with Mercury outboards and this issue? Any place I should start looking? Could something be getting wet that shouldn't be? Both times this has happened the boat was throughly soaked.
I have a problem with the switch on my throttle handle. Its a 2001 Mercury 150 Salt water Series. If I could replace the switch I would, its sort of molded in to the handle. I have thought of rewiring it and putting an aftermarket switch on the dash board. I just try to be very conscious of it and don't leave the boat unattended with the batteries on. It doesn't go on by itself but, hangs up on me.
I had a motor do that off and on for a while and then the trim motor just died one day... can't say for sure if it coming on by itself was a symptom of it being on its way out or not. Take your trim switch apart and see if it needs cleaning, maybe it's shorting in it.
1. Bamadeer's problem is probably with the plastic trim that sourrounds the trim thumb switch. I went through the same problem. Look at the plastic trim around the thumb toggle switch. Mine was hanging-up on the trim. I used a small hobby razor and trimmed about 1/32" of plastic away and never had another problem.
2. Fishesman, unless you are removing the cowling and soaking the entire motor, the problem is with the trim switch on the throttle. Water is probably entering the switch where the thumb toggle is located. Try drying it out first. Use a leaf blower then a hair dryer. Then, spraying some lubricant in the opening (like Corrosion Block).
Thanks LT, I will take another look at it. Is the switch replaceble.
There are probably different styles of throttle/trim handles. The Mercury has a plastic housing that surrounds the trim switch and thumb toggle. They are electronically melted or glued together at the factory. You can see a seam where they are put together. Cut along that seam with a razor blade (360 degrees) several times as you wiggle the plastic housing. The housing will eventually separate from the rest of the handle and expose the switch.
I did this to mine, thinking that the switch was malfunctioning. Then, determined that the plastic housing was not milled correctly at the factory and was causing the thumb toggle to hang-up.
I glued the plastic housing back with super-glue and it's been that way for several years.
If you can't repair that one go to bass pro or west marine. They sell them for 23-25 bucks and use a black ty wrap and put it on the handle right under the trim button. It works great. Usually three wires blue to the sky green to the ground and red/purple for 12 volts.+