Mercury 90 horsepower tilt

[Theenan]

A little stumped.
I have a 2014 Mercury 90 horse outboard.
The power tilt was not working. I determined that the motor was bad on the power till assembly. I ordered and replaced the motor and bench tested it with a 12 volt battery. The Piston drove up and down properly. I reinstalled the assembly and attempted to push the up and down buttons for the power trim. The relays just buzzed kind of a high rattling tone.
I disconnected the two leads to the power trim motor and verified that as I push the up and down the leads were delivering 12 volts as they should. After removing the power trim assembly a second time, I took the power trim assembly and touch the leads to the battery that was on the boat. Worked no problem. I then took the trim power assembly, laid it on the back deck (pontoon) of the boat and hook the leads back into the relay wires. The up and down relays just buzzed as before. Not knowing why the original motor smoked. All the wires were smoked up around the amateur etc and wondering if I have pitted contacts on my relays that may be causing the problem. Maybe as simple as replacing out the relays?
I'm also wondering what the third relay is for
Any help would be appreciated.

 

[wn6ngp]

A little stumped.
I have a 2014 Mercury 90 horse outboard.
The power tilt was not working. I determined that the motor was bad on the power till assembly. I ordered and replaced the motor and bench tested it with a 12 volt battery. The Piston drove up and down properly. I reinstalled the assembly and attempted to push the up and down buttons for the power trim. The relays just buzzed kind of a high rattling tone.
I disconnected the two leads to the power trim motor and verified that as I push the up and down the leads were delivering 12 volts as they should. After removing the power trim assembly a second time, I took the power trim assembly and touch the leads to the battery that was on the boat. Worked no problem. I then took the trim power assembly, laid it on the back deck (pontoon) of the boat and hook the leads back into the relay wires. The up and down relays just buzzed as before. Not knowing why the original motor smoked. All the wires were smoked up around the amateur etc and wondering if I have pitted contacts on my relays that may be causing the problem. Maybe as simple as replacing out the relays?
I'm also wondering what the third relay is for
Any help would be appreciated.

These relays do fail with time and use. I had to replace one on my 00/90hp. All they do when energized is to apply 12+- to motor to change directions. Just connect a light bulb(like an auto headlamp) instead of the motor and then measure the voltage to see if you get the proper toggle of 12v depending on up or down switch. It sounds like you have a wiring problem where invoking the trim causes the 12v for the relay coil to drop out then it goes back and forth, buzzing. You could have a bad 12v source or poor ground connections for the relay coils. You will want to look at the 12V going to the coils when you activate the trim switch. Measure right at the relay coils. Assuming you are losing voltage to the coil((s) then work your way back along the wires to see where the voltage is being reduced. Hopefully you have some kind or shop manual that shows how the wires are connected to the switches and motor.

 

[Chris1956]

Actually relays supply ground to the PTT motor, when not energized, and +12VDC when energized. They are different than solenoids.

However, you do need to check the wiring and especially the connections to make sure your relays get a good ground and good +12VDC for the secondary windings. The also need a good ground and good +12VDC on the primary winding.

 

[wn6ngp]

Actually relays supply ground to the PTT motor, when not energized, and +12VDC when energized. They are different than solenoids.

However, you do need to check the wiring and especially the connections to make sure your relays get a good ground and good +12VDC for the secondary windings. The also need a good ground and good +12VDC on the primary winding.

that is correct, those relays have to be able to swap + to - in order to make up or down trim motor. The problem could be that the voltage going to the relay coils can sag or be temporarily interupted which sounds like what is happening if the relays can be heard charttering.