Tilt/Trim goes up without command

[garland gaston]

My 115 hp 1996 Merc trimmed all the way up without being commanded while dry docked. Had to disconnect battery to get it to stop. I replaced both relays with new items. Seemed to correct problem. About 8 months later same happened while running on water. Disconnect battery again to stop motor from running. Manually lowered engine and disconnected trim relays to get in. (50 miles from ramp). Removed and opened up the "up" relay. Relay is molded, but can be cut open. Contacts looked new, no pitting or arcing. Normally open spring was good. I think it must be one of the rocker switches commanding relay to close. Any ideas? Is there something else that could cause this problem?

 

[alldodge]

I think it must be one of the rocker switches commanding relay to close.

Agree, this is where it probably is. Same thing happen to my I/O, need to replace the switch

 

[Chris1956]

Rain water can get into the rocker switches, puddling across the lower contacts, causing the trim to go up. Blow the water out with WD-40 and see if she will behave.

 

[Chigwalla]

Yep, it's usually the trim switch in the control.
You might want to run with it disconnected for a while just to confirm it's not the cowl switch or the transom switch (if equipped).

 

[garland gaston]

Thanks all. Good suggestions. I'll give them a try and let you know the results.