2003 75HP mercury Tilt trim issue.

[James R]

Tilt trim operates on its own going fully one way or the other. The motor continues to run until the battery is disconnected.
After which the tilt trim no longer works. Examination revealed that the positive terminal on one of the harness relay sockets had overheated and melted the plastic of that pin connection in the socket. Prior to this the tilt trim was working normally from both the remote control and the switch on the motor cowling , Replaced the harness and relays and all was well until a trip on the lake whereupon the same failure occurred burning a relay socket on the replacement harness. Wiring appears to be good and the switches both function normally. Something seems to be activating the tilt trim and it may be that the continuous running of the pump motor is causing the socket to overheat.


Any thoughts on this would be appreciated..

 

[Texasmark]

Up is sky blue, down is grass green....PTT wiring. You have a welding/welded closed contact in the relay that controls the direction that you are having a problem. When the PTT hits a limit, an unloader valve inside the unit releases pressure (pop off point) while the motor still runs the pump. You the operator sense that you are at a limit and let go of the UP-Down button you are using for control and the control relay opens and shuts off the motor. With a welded contact inside the affected relay, you can't interrupt the circuit because it is welded closed. You can swap relays for a test to verify what I said.

Sometimes, as they are becoming welded they will work ok, but then after they heat up, they weld.....or they are already permanentlywelded. Common problem with mechanical relays.

 

[James R]

Thank you for your response. I am familiar with the tilt trim systems and some of the problems but this failure is completely new to me. There has been some suggestion that water getting into the switch on the motor cowl will cause the tilt trim to activate in this manner.
Continually replacing harness and relays is not going to get to the root cause.
Any other thoughts?

 

[Texasmark]

Agree on water in a switch, as age and usage increase, are bad for switches.....anything that causes a conductive path to develop between the contacts is suspect. Your relay check is as simple as swapping relays. While you are there, examine the connections on the relay pins as some of what you mention may be there also.

 

[James R]

Thanks for your input.
I have now replaced the harness and relays and disconnected the cowl mount switch. Will try on the water one more time.