F225txrc and DES switch question - Rodbolt? Boscoe?

[fairdeal]

My dual/multi engine knowledge is sadly weak/non-existent

I "know" that in a multi-engine arrangement,
when one engine goes into rpm reduction, the others do as well
presumably via the "DES" - Dual Engine Switch

but exactly how?
According to the ECM diagram in the F225C SM,
the DES "shares a connection" with the alarm horn wiring -

I thought the ECM simply provides a ground to activate the warning horn

how does one engine ECM close the DES?

how does the other engine ECM "know" that the DES switch is closed ?

[99yam40]

Does this have to do with the F225TXRC single motor with the duel switch being on in the other thread?

[fairdeal]

Does this have to do with the F225TXRC single motor with the duel switch being on in the other thread?

I suspect it may...

[boscoe99]

Twins and trips are tied together via a control module in the switch panel. If the CDI/ECU of one motor tells the module that it has a problem (for instance to sound the alarm buzzer for the problematic motor) the module also puts the other motor into RPM reduction mode. The module tells the CDI/ECU of the good motor. The good motor then goes into RPM reduction mode.

A CDI/ECU normally applies a ground to the pink wire to cause the buzzer to sounds. When the pink wire is grounded by the module (and not the CDI/ECU itself) the CDI/ECU sees that ground as being set by the Dual Engine System. It knows it did not apply the ground. So it must be coming from the DES.

I think.

[fairdeal]

A CDI/ECU normally applies a ground to the pink wire to cause the buzzer to sounds. When the pink wire is grounded by the module (and not the CDI/ECU itself) the CDI/ECU sees that ground as being set by the Dual Engine System. It knows it did not apply the ground. So it must be coming from the DES.

I think.

that's what puzzles me.
If the ECM schematic I posted above it correct...

trying to think this out -

"normally" at key on (and while running) the ECM will have ~12 V at Pin #3 -
which, "whenever it wants to" - it could connect to ground to sound the buzzer

BUT - if it is running - and the DES connects the buzzer to ground -

then the voltage at Pin #3 will drop - to zero? near zero?

and the ECM then knows that "the DES switch is on"

I suppose that's it...

[boscoe99]

Have you measured the pink wire and found it to be at 12 volts?

[rodbolt17]

ok.
simple DC circuit.
turn on the key, yellow wire to ground potential is 12v.
yellow goes to the honky horn.
honky horn was just a coil of wire, now it is solid state but about the same.
coming out of the honky horn the insulation is now pink.
now it heads for the motors.
at the engine it simply hangs out until a switch triggers,once closed the ECU sets a ground path.
the actual triggering of the second engine is done by the des module behind the dual engine module behind the key switch panal.
if you hooked a meter between the yellow wire and ground at key on you would read battery voltage.
if you then tripped a switch you would now read the voltage drop acrossed the horn.
see how simple DC circuits are?

[boscoe99]

It was so simple like the jitter bug
It plum evaded me

[rpambrun]

But, but, but....how do you shut the damn thing off on a single engine scenario if the pink wire doesn't show a grounding somewhere?

[rodbolt17]

you don't. like I said it is a translation issue.
a more accurate description should have been buzzer on switch.
the actual DES is con*****ed by a module behind the dual keyswitch assy.
the pink wire GETS grounded inside the ECU.
remember it is a stupidly simple DC circuit.
yellow from the key,through ye ole honky horn to the ECU. now it waits on a trigger .
the ECU is monitoring various switchs and battery voltage.
once the ECU sees an issue it applies a ground path for the pink wire.
Yamaha calls this ground DES on.
it should be alarm or buzzer on.