How is the trim limit switch supposed to function?

The Ors

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Hi there, I've been registered here for a couple of years & had lots of help from reading other's posts but this is my first post, so 'Hello' to everyone.

Anyway, as per the title, how is the Mercruiser trim system intended to function?

I have a 1991 Mercruiser 350 Mag/Alpha one. When I bought it the trim switch in the Commander controller was broken & had been replaced with a rocker switch on the dash. The trim gauge did not work & the trailer button did not work. Pressing one side of the rocker switch moved the leg up from any position to as far as fully up; pressing the other side of the rocker switch moved the leg from any position to as far as fully down.

When I had the boat out of the water I replaced the trim sender & trim limit switch. the trim gauge now functions correctly, the trailer button will move the leg up from any position to as far as fully up & the rocker switch functions as previously.

Is that correct? I was under the impression that the trim up button should only move the leg up a certain amount (not fully), in order to protect the UJ.

I suspect that a previous owner may have altered the wiring in order to overcome a broken limit switch but I wanted to check what is actually supposed to happen before I go altering things.

Cheers

Darren
 

alldodge

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42,640
Hi there, I've been registered here for a couple of years & had lots of help from reading other's posts but this is my first post, so 'Hello' to everyone.

Anyway, as per the title, how is the Mercruiser trim system intended to function?

I have a 1991 Mercruiser 350 Mag/Alpha one. When I bought it the trim switch in the Commander controller was broken & had been replaced with a rocker switch on the dash. The trim gauge did not work & the trailer button did not work. Pressing one side of the rocker switch moved the leg up from any position to as far as fully up; pressing the other side of the rocker switch moved the leg from any position to as far as fully down.

When I had the boat out of the water I replaced the trim sender & trim limit switch. the trim gauge now functions correctly, the trailer button will move the leg up from any position to as far as fully up & the rocker switch functions as previously.

Is that correct? I was under the impression that the trim up button should only move the leg up a certain amount (not fully), in order to protect the UJ.

I suspect that a previous owner may have altered the wiring in order to overcome a broken limit switch but I wanted to check what is actually supposed to happen before I go altering things.

Cheers

Darren

Howdy Darren

Your correct, if the trim systems is connected and working correctly the trim button only allows it to go up a given distance. Here is a link to the trim system
http://web.cemr.wvu.edu/~mathews/boa...20Eighteen.PDF

And a pic
Trim wiring Merc 2012.jpg
 
Last edited:

nola mike

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Apr 22, 2009
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You're correct, the trim switch only raises it a certain amount, while trailer raises it all the way. Limit switch determines how far the trim switch will raise the leg. Common to bypass the limit switch if it's bad, so the trim button will still work in the same manner as the trailer button.
 

stonyloam

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Mar 13, 2009
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OK the trim limit switch has two parts, the movable part attached to the gimbal ring and the fixed part attached to the gimbal ring pivot pin. The movable part has a arc shaped copper bar, and a contact in the fixed part rides on that bar. When you push the up trim voltage travels through a purple/ white wire through a connector on a black wire to the contact, into the copper arc, out through a black wire to a connector with two blue/ white wires, on to the up solenoid of the pump. As the outdrive rises the copper arc moves under the switch contact until it reaches the end, contact is broken and the motor stops, limiting the amount that you can raise the outdrive. The trailer switch is attached through one of the b/w wires to the connector and directly to the up solenoid, so it will run without limit. What your PO probably did was bypass the trim limit by attaching the purple/ white wire directly to the two blue/ white wires in the connector.
 

The Ors

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Aug 31, 2013
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Brilliant! thank you all for your helpful replies. So, I've either set the trim limit incorrectly or the previous owner played with the wiring. My money is on the second option (I was very careful to follow the manual when I fitted the switch :)).

Some more investigation required then...

Darren
 

stonyloam

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Mar 13, 2009
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If you plugged one black trim limit wire into the purple/ white wire, and the other into the connector with the blue/white wires then I suspect the PO wired the up terminal of the rocker directly to the b/w wire. What you probably need to do is find the end of the p/w wire and attach it to the up side of the rocker, then add a rocker for the trailer. Pick up power from the other switch and wire the new "trailer" switch directly to the b/w wire. Good luck.
 
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