I believe the Yamaha service manual will have that wiring diagram.

your local Yamaha dealer should able to get you one if you do not have one already.

Or look up the manual # here you need and then do a search on line YAMAHA MANUAL STORE

First thing that needs to be done is to get the model identity straightened out. It is an F75TLR. If you mention a 75HP Yamaha you might get pages from a two stroke service manual.

As noted, you can either buy the complete manual (preferred) or perhaps if you have a good relationship with your dealer he will give you a copy of the wiring diagram. Also ask him for the pages that depict the procedures to test the trim and tilt switch and the relays.

Why does anyone try to work on or troubleshoot a motor without having the necessary documents in the first place? If you were an aircraft mechanic you could (a) lose your job (b) get fined (c) go to jail (d) lose your license (e) cause someone to get hurt or die (f) cause some expensive equipment to become damaged, or worse.

part of that is true for an outboard or marine tech.
my customers sometimes go 50-60 miles offshore and stay a day or three.
my repairs and troubleshooting skills are either correct or someone may die.

that's why my motto is"I don't care if you go out. I do care that you come back"

A good motto for sure. It is nice to know that a gruff ole bastard cares.

Put your troubleshooting skills to this snippet from a Yam diagram and tell me what you see?

Thanks everyone for your replies. Unfortunately, the closest Yamaha dealer is at 6 hours of airplane from here so going to a dealer is impossible and I have to do my own repairs. Thanks Boscoe99 for the diagram but this looks like a pre 2006 model with an independant trim relay for the up and one for the down. The diagram I would need is for a 2008 F75TLR which only has one relay that do both the up and down. It would really be much appreciated if you have that same wiring diagram for my model!! Thanks

The diagram was not intended to address your model. It was a puzzler for the purported prince of mechanics, Rodbolt.

as long as the black wire that's exiting to the right is grounded the circuits would work

what is shown is typical of a four stroke circuits for trim and start.
#4 is a slave solenoid that triggers the starter solenoid.

now is where the diagram gets funny.
whats NOT shown is the FACT that at REST BOTH the motor OUTPUTS are taken to GROUND.
apply a voltage on either the Sb or the Lb inputs moves the contacor to apply 12Vpositive on either the blue motor or green motor outputs,the OTHER relay is now the motor ground path.
the B/W wire is typically brown in the US market between relay #4 and the start solenoid.
its typical of most japanese diagrams that tend to NOT color code nor show the actual connector.
they have progressed over the years but???

however this circuit for the trim is electrically the same for BOTH the twin relay AND the single relay trim systems using a two wire motor.

the ONLY reason a relay is needed is to save space weight and money.
it allows the use of a small current,typically less than 3 amps, to control a large current of between 25 and 40 amps(trim motor load).
but its the same circuit design used by Volvo with hydraulic trim and the old OMC and BRP stuff since the 80's
on most any two wire trim motor setup when one relay is triggered its output is + and the other relay remains the motor ground path.
whats not clearly defined in that diagram is the ground paths.however they do exist.

Here is more détails on my problem.. I hope someone will know what is causing it. I can only trim my motor down, the up doesn't work anymore. I did several tests already. I know the trim motor is good since I unhooked the blue and green wire from the trim relay (big ones going to the motor) and was able to make the motor go up or down by applying them directly on the battery terminals. I know the relay is good since I tested it in another motor and it works normally. I also tried unhooking the small plastic terminal with the light green/sky blue wires from the relay and apply 12V on either the sky blue or pale green wire and motor trim fines this way. When I test the circuit continuity from the other end of that little plastic plug, everything works fine when the battery is not hooked to the motor: both the switch on the remote and on the motor itself work normal, and give continuity between the red and sky blue wire when I press up and continuity between the red and light green wire when I press down. The problem arise when I connect my motor to the battery. Now, when I press the up button, there is current going in both the light blue AND pale green wires while the down button only gives current to the light green wire as it should.. Any idea what could cause this??? Thanks so much for your help! I'm out of idea!

My guess would be a failed diode.

my guess is the relay failed.
hook up a digital meter to both motor output terminals.
hit the button up, then down.
you should see 12V+ in one direction a -12v in the other.
like I said the relay is a polarity reversing device.
the side NOT going 12+ remains the ground path.

Relay is good. I tested it and it works fine on its own. The problem is that both the green and blue wire gets +12V when I press up instead of the green wire getting -12V. When I press down, it works fine as you said, +12V on the green, -12V on the blue.

then the relay has failed.
unhook the motor wires.
test the motor output terminal to ground.
both should show continuity.
at rest BOTH terminals are grounded.
at rest the volt meter should read 0v,when triggered UP it will display a voltage,then trigger it down and you should see the same voltage with a reversed polarity.
don't move the meter leads for this test.

Methinks the blue and green power wires are getting confused with the blue and green control wires.

Easy enough to test the relay and the diode assembly to verify where the actual problem lies.