1980 Mercury 115 power trim wiring

[eggs712]

On my '80 Merc 115 with the separate trim motor, I recently added a newer style throttle control.



The wire colors didn't all match up and I couldn't find the wiring diagram for the control box, but the tachometer works. I had the trim motor out of the boat at the time because the hydraulic hoses were rotten. The new hoses are now installed, and I also had to redo the wiring (was rotted) that goes to the tiny red switch that mounts on the motor.



Now when I reconnect the battery, the trim motor immediately comes on as soon as it touches a battery terminal. I think the switches in the control box are good, so I either did the wiring wrong or messed up the little red switch when I reinstalled it. Any ideas on how to fix this?

 

[merc850]

That switch circled is the tilt limit switch that you set for max trim after you set up the motor; this diagram is for the 3 button switch panel so you might have to add a switch for trailer mode.

 

[eggs712]

Thank you, I downloaded that image and will try to figure this out this afternoon. One more question, why does the newer harness have four wires coming out by the motor?



They look the same color as trim wires, but I currently have the 4 wire harness from the trim motor running to the control box. Should I be using the four wires shown taped off, or are they for the later style trim motor?

 

[eggs712]

Update: with the limit switch disconnected, everything works properly. Is there any reason to even worry about the limit switch if I don't have a trailer button on the control box?

 

[merc850]

You can set the limit so that you can trim the motor out and it will stop before cavitation, makes it easier to control.

 

[jimmbo]

The purpose of the limit switch was to prevent the engine from being trimmed up/out to where the swivel bracket/yoke no longer had the transom bracket to prevent horizontal)port/starboard movement. That was why the old twin ram power trim system had a separate Trailering button to raise the engine higher

 

[eggs712]

I took the boat out for a couple hours Sunday to test the power trim, and ran into some issues. The trim itself worked good, and there were no leaks with the new hoses.

However, an alarm in the control box would go off almost constantly. The only thing that made it go off for only a second was tapping the 'up' or 'down' trim button, but it would come on again as soon as the throttle moved even slightly. My motor doesn't have any low oil or temp sensors, and this only started after plugging the trim motor back into everything.

Anyway, I finally found the general wiring colors for newer Merc parts, and I had two wires wrong into the trim wiring harness. Without a trailer button currently, I only needed the green and blue wires from the control box. So I clipped the two unneeded wires off tonight, and hopefully that solves my problem.