CONTINUOUSWAVE

I just bought and rigged a used 2005 Yamaha F90 with a new Yamaha 704 controller and an OEM Yamaha 10-pole wiring harness. The power trim is not working correctly.

The F90 engine will down trim from the trim DOWN switch on the cowling and from the trim DOWN switch at helm. When the trim UP switch is depressed it just "clicks."

NARRATIVE OF SOME TESTS PERFORMED

I have disconnected the BLUE and GREEN 10-AWG conductors that run to the trim motor from the trim relay. Using a good battery I confirmed that the trim motor will operate in both directions.

The trim relay functions correctly and operates the trim motor in both directions WHEN the two-pole connector with LIGHT BLUE and LIGHT GREEN conductors is disconnected and 12-Volts is jumpered to each pin.

However, when testing the two-pole connector with LIGHT BLUE and LIGHT GREEN with a Voltmeter, I get the following:
--when operating either the helm trim switch or the cowling trim switch in the DOWN position, I get 12--Volts on LIGHT GREEN.

--when operating either the helm trim switch or the cowling trim switch in the UP position, I get 12--Volts on both LIGHT GREEN and LIGHT BLUE.

I suspect the cause if this unusual outcome is a bad switch.

I disconnected the 10-pole boat harness from the engine at the side of the engine and retested. There was no change, that is, there was still 12-Volts on both LIGHT BLUE and LIGHT GREEN conductors when the cowling switch was operated in the UP position.

Then I disconnected the cowling trim switch and re-connected the wiring harness to the remote controls, Repeating the tests produced the same outcome: there is still 12-Volts on the both the LIGHT BLUE and LIGHT GREEN at the connector before when operating the helm control trim switch in the UP position.

I also tested each trim switch while engaging up and down with an Ohmmeter to see if I could find an obvious short between LIGHT BLUE and LIGHT BREEN conductors, but I could not detect a short circuit.

I de-rigged the boat harness and tested [for continuity] across each pin--especially the trim wires--and could not find any obvious sign of a short or connection across any of the wires.

From other write-ups this all leads me to believe there is a wire defect between the 10-pole connector on the side of the motor and the two-pole LIGHT BLUE and LIGHT GREEN connector for the trim relay.

Before I go cutting up an otherwise good Yamaha wiring harness I have to ask:

Q1: am I missing anything?

Q2: Is there anywhere else these trim wires come together?

Q3: Could one or both trim switch be bad but not show on an ohm check?

Any help appreciated.

ASIDE: I am a long-time reader; this is my first post. I have a 1987 Newport 17' that I just finished re powering with the Yamaha F70 engine under discussion.

From my experience with a very old c.1987 Yamaha engine that I owned, the owner's manual included a schematic diagram showing the wiring of the engine, the wiring harness, and the remote controls. If this 2005 Yamaha F90 engine you have came with the owner's manual, perhaps there is a wiring diagram illustration in the manual.

Having a schematic diagram of the wiring allows a better understanding of the circuitry.

In some applications there are two separate trim relays, while in other applications the two relays are combined into a single assembly.

There is a general trend with power trim circuits that the solid green and solid blue conductors (which are the 10-AWG conductors) are the high-current circuit that delivers the battery positive and battery negative to the engine's trim motor via the trim relays.

The coils of the trim relays are operated by a low-current circuit carried on the LIGHT BLUE and LIGHT GREEN conductors. As you can see in the diagram, it is possible to have more than one switch controlling the coil, as the circuit allows for a second (or third) switch to just be wired in parallel with the first. The COMMON of the switch can get its 12-Volts from any source, so there is not a dedicated third wire included to carry the 12-Volts to the remote switches.

There is a common standard for the insulation color coding as follows: BLUE is for UP as toward the sky; GREEN is for DOWN as toward the earth.

There is a common circuit arrangement for the power trim. I cannot say for certain this will be used in your engine, but the circuit is so simple and has been used for a long time, so there is a good chance it will be used in this c.2005 Yamaha engine.

First, let me show a very simple drawing of the usual and very common power trim circuit. It is quite a crafty implementation of the control circuit and uses a minimum of wiring and just two single pole relays.



As shown in Figure 1 above, the engine trim motor is connected to the COMMON pole of each relay. When both relays are NOT energized, the result is both the BLUE and the GREEN circuit to the motor will remain connected to battery negative by the NORMALLY CLOSED contacts of the relay, and there is no voltage applied to the trim motor. As a result the trim motor does not operate.

When the relay associated with the GREEN conductor--which is called the DOWN RELAY--is energized, the GREEN conductor is then connected to the NORMALLY OPEN contact of the relay, which is the 12-Volt battery positive, resulting in the trim motor getting 12-Volts applied, and causing it to run in the DOWN direction.

When the relay associated with the BLUE conductor--which is called the UP RELAY--is energized, the BLUE conductor is then connected to the NORMALLY OPEN contact of the relay, which is the 12-Volt battery positive, resulting in the trim motor getting 12-Volts applied, and causing it to run the UP direction.

The best INFERENCE I can make of a possible cause of the problem is that the relay associated with the UP direction has failed, and its contact remains stuck in the normally-closed position even if the coil is energized, or the coil has failed and the relay never energizes.

The next test to make will be to disconnect the 10-AWG BLUE and GREEN conductors from the trim trim at the relay. Check that with both relays de-energized you get continuity from the COMMON to the NORMALLY CLOSED pole in both relays. Then energize the UP relay and determine if the COMMON of the relay remains connected to the NORMALLY CLOSED pole.

It is possible for the mechanical contacts in a relay to become fused together, and the power of the coil may not be sufficiently strong to break apart a fused contact. It is also possible there is a poor connection for the coil circuit in either the positive or the negative, and the coil never actually gets energized.

Thank you for your detailed response Jimh. I do have an owners manual however at least the one I have doesn't have much for wiring schematics. I tried the test you recommended and found the following; 10g blue and green disconnected from the relay with relay de-energized I have continuity from common to the normally closed pole on Up and Down relays respectively. When energizing the up relay from either trim switch I loose continuity to normally close/ground and have 12v+ at the up relay. When energizing the up relay I also have 12v+ at the Down relays normally closed pole and no continuity to ground.

It seems the relay is doing what its told in the sense that I have 12v+ at the light blue and light green wires with the up trim circuit energized and also 12v+ at the up relay and down relay normally closed poles. Additionally I tested the trim with a brand new Yamaha oem relay this morning and I have the exact same results. I also test a 40$ amazon relay just for kicks and same results. It seems that 12v+ is getting into the light green wire only when the up relays is energized somewhere between the switch(s) and the relay.
Thank you again for your help.

17newport--I am happy to see your rapid reply to my comments. Often I write a thorough reply and the originator never returns to acknowledge anything.


Regarding why the trim motor is not operating in the UP mode: my initial assessment was that the UP relay was not actuating or was stuck, with the result that both motor leads were still connected to the battery negative, and thus the trim motor does not run.

Interestingly, the same outcome occurs if BOTH the relays actuate, that is, both relays are energized and connect their BLUE or GREEN leads to the battery positive. The result is also the same, the motor does not run (because there is no difference in the voltage across its terminals).

At first glance the method for both relays getting activated cannot be a simple short circuit. Here is why:

--if there were a short circuit in the wiring that caused the UP relay coil circuit to also actuate the DOWN relay coil circuit, then that short would work all the time, meaning that there would also be no DOWN trim possible, either. A short circuit works all the time.

--in order for there to be a possibility that the UP circuit can also actuate the DOWN circuit but not vice versa, the connection must be made through a DIODE. A diode allows current to flow only in one direction. So the diode must be in the circuit for the DOWN relay coil (the LIGHT GREEN) and must be connected in such a way that it is also powering the circuit for UP relay coil coil (the LIGHT BLUE), but the diode blocks current in the UP relay coil circuit from passing through to the DOWN relay coil circuit.

Figure 2 is a sketch of how the diode would be connected between the LIGHT GREEN and LIGHT BLUE wires at the trim switch. The orientation of the diode is important, as it only conducts in the direction of the arrow, so as drawn below, it only operates both relays when the UP switch circuit is energized. Also, the diode only needs to be at one switch as the circuits for the two switches are in parallel, so the diode is in the circuit for both switches.



Take a look at the wiring and look for a diode connected somewhere. This has to be the most reasonable explanation.

The beautiful property of electricity is that it always follows the same rules for flowing--it flows in any way possible if there is a path, and not just in the path your were expecting it would flow.

This may actually be possible because I believe that there may be a diode included in the rigging (or on the engine itself) to permit the operation with TWIN engines so that it is possible to trim each engine individually, one at a time, or to trim both engines in unison. Because you bought this engine as a used engine, perhaps the engine was at some time used in a twin engine rigging and there might be some strange diodes incorporated in the wiring.

UPDATE--OOPS, I drew the diode in the wrong direction, so I just replaced Figure 2 with Figure 2a which shows the correct orientation of the diode. Most diodes are marked on their exterior with the arrow (anode) and bar (cathode) symbol to permit identification of the anode and cathode. Direct current flows in the direction of the arrow, that is, from the anode to the cathode.

Thank you Jimh I really appreciate your thoughts on this as I’ve been struggling to think of what I’m missing. Great thought on the diode. I was wondering about a diode and hadn’t considered the dual motor scenario. I was thinking maybe there is a diode wherever the 3 wires for the helm trim and 3 wires for the cowl trim switch come together as I think there must be some way to protect the trim circuit from actuating both twin switches at the same time…

thank you again for your help ill start trying to back track and find a diode in that wiring. I’ll update when I find it but it may be a week or two with work getting in the way!

To discover if there is an diode in the wiring will be quite interesting. I await your update, but I understand it may be a while.

There are two diodes on the 2005 Yamaha F90 tilt/trim wiring. They are located in a small black plastic cup which can be found taped to the vertical section of the main harness trunk that runs just inboard of the fuse cups under the cowling. I believe these diodes are transient voltage suppressor diodes "TVS" that are designed to shunt voltage spikes (which can occur when the tilt/trim relay opens and closes) to ground which protects the ecu from voltage spikes. The OEM Yamaha solution is very compact and the two diodes rest on a small circuit board which are connected to ground on the back of the board. After removing the silicone you could see where one of the wires to ground was burnt and interestingly the diode for the trim out (blue) tilt/trim registered no resistance with a multi meter while the trim in (green) side diode had measurable resistance. This matched my symptoms of having normal trim in function but no trim out at either switch and 12v+ at each end of the tilt/trim relay output when trim out (blue) circuit was engaged. Essentially the diodes are connected together, then connected to a common ground. The path to ground was burnt after the two diodes merge, and the trim out (blue) diode had broken down and offered no resistance which allows it to pass 12v+ straight to trim in (green) diode when power was applied to the trim out circuit.


**Disclaimer proceed at your own risk and do your own research. I am a DIY hack with no formal knowledge or experience. I can not recommend doing this work on your boat and am posting this as an interest piece only. I performed this work on my own boat as the other option was to buy a new harness which I did not want to do. I would recommend taking your boat to a qualified professional which is undoubtedly smarter (and faster) than doing all the research and work yourself...**

My current solution was to wire two TVS diodes into a small harness which connects to the main harness where I cut the OEM diode back off. It is three wires blue, green and black. It is difficult to find TVS diodes with a narrow working and clamping range so I settled on the ones below which have a working load around 13v, max breakdown of 15v and full clamping load around 21v. The full clamp is higher than I would like but the next smaller diode (5KP12A) risks partial clamp when running full rpm and full charge while adjusting tilt/trim.

The tilt/trim does work with the OEM unit simply cut off but I didn't want to run the boat for too long without voltage protection for the ecu. I purchased several TVS diodes from Digi-key.com, I ended up using two from a company "Little fuse" the model was;

5KP13A
5KP13ACT-ND
TVS DIODE 13VWM 21.5VC P600

I have attached a couple pictures below. It ended up bulky but has worked for me for the last couple months of the season. I did purchase some different size diodes to try if these fail. I will follow up with this post if I end up modifying this setup or if it goes pear shaped...