250 HPDI gauges/warning horn

[Nine Shots]

I recently installed a 2003 250 HPDI model Z250TXRB-60VX on my bay boat. The motor had a dressed power head installed in 2008 and has 80 hours on it. I have fairly new generic analog gauges including a new ignition switch so my mechanic spliced into the Yamaha harness at the helm and hooked up the gauges and ignition switch. Everything works, motor starts/runs good....except he failed to install the warning horn that I saved from my Mercury harness.

I took it back to the shop for installation of the warning horn. He hooked the purple wire on the Merc warning horn to the pink wire at the helm end of the Yamaha harness and black to ground. The warning horn comes on when the ignition switch is turned on and remains on, even after the motor starts.

The mechanic, who is one of the best in this area, and I have now been trying to get this straightened out for 3 weeks to no avail. With the ignition off, there is no voltage on the pink wire at the helm. However, even with everything unhooked except the main battery cables, there is voltage on the pink wire at the head sensors. There is no continuity across the sensors. He says there should be no voltage at the head sensors until the ignition is on and when/if the sensors close to ground the horn should blow. He has talked to the Yamaha mechanics at the dealership(s) but they are clueless.

I'm beginning to think there should be voltage on the pink wire at both the head sensors and the helm end of the harness with a separate ground wire (maybe thru the ignition switch) back to the sensors so that when/if one closes completing the circuit back to ground, the horn would blow.

The mechanic now thinks we may need to install a Yamaha ignition switch but there is none in town. He ordered one 10 days ago but its not it yet.

I certainly don't want to run the motor without the warning horn. I would appreciate any help/advice on this before I give up, pull the motor off and wave the white flag.

[boscoe99]

In a Yam control box or key switch panel the buzzer is normally powered by the yellow wire. That is, it has 12 volts applied to it when the key is turned to the on position. Mercury uses purple for key on power. The buzzer is normally ungrounded.

The pink wire to the buzzer is the ground reference wire. If and when a thermoswitch closes, or the ECU grounds the pink wire due to low oil in the main oil tank, then the buzzer will sound.

[Nine Shots]

Thanks for the reply. I spoke with the mechanic this morning. He had/has the buzzer hooked to the yellow and pink wires. He borrowed a Yamaha switch panel from another boat yesterday, but the buzzer still goes off when the switch is turned on. He now thinks there is a problem with the wiring harness but won't have time to troubleshoot that until next week. This motor ran fine on the boat it was on when I bought it and we had no trouble removing it from that boat or installing it on my boat so I don't think it was damaged in the transfer.

Any other thoughts?

[rodbolt17]

I think he is either hooking it up wrong or some of the piezioelectric horns just wont work or you have an oil tank,engine, switch or a temp switch issue.

at the ign switch in the ten pin main,yellow is 12V to the horn positive(purple) and pink will be the ground path,engine.

don't confuse the 10 pin pink with the 4 pin trim harness pink.
two totally separate circuits.
Yamaha has NO self test function at key on power.

[Nine Shots]

Finally getting back to working on the boat. My boat has a Yamaha top mounted control box with only a tilt/trim switch. We borrowed a side mount control box with ignition switch and plugged the harness into it. Everything worked as intended. Apparently my wire harness is OK but there is a compatibility problem using the generic ignition switch and the external Merc warning buzzer. Close to waving the white flag. I hate to now have to buy Yamaha gauges, switch panel and control box.

[boscoe99]

You may be overthinking this issue. The horn is simply miswired. You don't need to buy anything.

All that needs to be done is to have 12 volt positive power applied to the warning horn. Could be a Yamaha yellow wire or a Mercury purple wire. They are both "key on" power. This means that positive power is applied whenever the key is in the ON or Start position.

Attach the pink wire in the Yamaha ten pin harness to the ground side of the horn. I can't really recall but don't think the buzzer is polarized. There should be two terminals on the buzzer/horn. Yellow/Purple wire to one side and the pink wire to the other side.

When the motor is running it will have 12 volts on it. If and when there is an over temperature event or a low oil event the ECU will apply a ground reference to the pink wire. The horn will now sound.

[99yam40]

As Rodbolt17 said I have read about a non Yamaha horn causing bleed through problems before, so do not rule that out all together after checking everything else.

But it was one from Radio Shack from what I remember