What is this part?

I was adding some grease in the zerks on a 1978 Mercury 1150 and noticed this. According to the manual it has something to do with the trim limit adjustment and I also noticed that it's missing on the other side of the motor. It looks like it has mounting holes for this, but the part is not there on the other side. The power trim system seems to work fine. Is the power trim motor supposed to stop on its own after it's raised or lowered to a certain point? TBH, I just let go of the button to stop it.

It is a Trim Limit Switch. The Early style of Power Trim, the one you have, used it to limit how far the Motor could be Trimmed out. The Original Trim Tilt Control was on the Dash with 3 Buttons.

The Center Button, would raise the motor up to where the Limit Switch would cut off the Power. Too tilt the Motor higher for low speed shallow water operation, or to raise it up fully for Trailering, both the Center and the Top Buttons had to be pressed and held in

In about 78 Merc brought out new Remotes that had the Trim Switches in the Throttle Lever, but used a Separate Button for Trailering.


In the early-mid 80s this Style of Remote Lever was used on the Motors that used the 1st gen Power Trim


There is only One Limit Switch used, the Rams were the same for both sides of the motor, so there would be an unused mounting location on the Ram on the other side

Yes, that is the trim limit switch. A lot of them are broken by this point and need to be bypassed to use the SPDT PTT switch on the newer controls, vs the original 3 button control panel.

I just have 2 trim control buttons on the throttle lever, and they will trim all the way down or all the way up to trailer. So, it seems like they have been bypassed at some point, and my remote control has been updated as well. The trim stays put when under way wherever I set it, so looks like I can just safely ignore the limit switch on the motor. Thanks for that info!

The Limit Switch is there to prevent the Motor from being trimmed high enough to be lacking the Lateral Support provided by the Transom Brackets, so be careful how far out you trim it under speed

jimmbo said:

The Limit Switch is there to prevent the Motor from being trimmed high enough to be lacking the Lateral Support provided by the Transom Brackets, so be careful how far out you trim it under speed

Click to expand...

Yep, good advice...thanks! I always stop and trim back down if I hear the prop start to cavitate. It really doesn't need a whole lot of up trim to get in that sweet spot! This is where a trim gauge would be helpful although the angle would change depending on how the boat is loaded and not sure how easy it would be to retrofit a sensor on an old motor like mine.

While a Trim Gauge was an option available on the 2nd generation of Power Trim introduced in 1984 on the I6s and the 66 cu in 4 cylinder, there was never One offered for the Unit your Motor has.

Most boats will ventilate before the motor is trimmed beyond the transom brackets. You could check yours for this.

Load her normally. Cruise at a usual speed. Trim up until the prop ventilates. Kill the motor and see how far she is trimmed up.