225TXRP: question about thermosensor Assembly

[carboncow]

We are going to put a new digital tach on and old (1991) 225 engine. I've been told that the engine doesn't have a sender that will trigger the newer tachs over heat warning buzzer.

The next option would be to install an analog gauge and I'm curious to which of these options is the way to solve this need.

1. Tap off the thermosensor assembly (6R5-85790-00-00) or
2. Put a new temp sensor (somewhere?) in the block to wire the new gauge

Or is the premise wrong from those who have told me there is no overhead buzzer sender?

[boscoe99]

From what I see the motor will provide an over temperature signal to a tachometer that has this function embedded within it.

The buzzer should sound and the motor should go into RPM reduction mode however with or without a tachometer even being installed.

[carboncow]

Boscoe,

Thanks...this is what I was hoping and figured as long as there was a sender switch (which we know there is) and the tach will receive a signal I can make it work. Regrettably I'm getting so much mixed info from the two top parts suppliers out there and was hoping you guys would chime back in.

I'll assume the buzzer will come from the ignition switch (assuming that buzzer works). Does the tach make an audible sound too or just the symbol when it gets an overheat signal?

[boscoe99]

The warning buzzer gets its 12 volt power and the ground to make it sound the alarm via the main engine ten pin harness. The ten pin harness also provides 12 volt power, ground and the tachometer signal to the tachometer.

With respect to tachometers that have warning lamps/lights/icons an additional harness runs from the motor to the tachometer to provide a ground for what ever lamp/light/icon needs to be activated. This additional harness also provides the trim signal for either a trim gauge or the multif-function tachometer that has a trim bar scale on the side of it.

If you get a copy of the service manual that is applicable to your model motor you can see all of this in a wiring diagram. It shows the two thermoswitches being wired to both the CDI (for RPM reduction mode) and also to the wire harness that runs to a tachometer or light panel on the dash to activate an over temperature light.

[rodbolt17]

dude, dunno who tole ya whats buts ya needs to find a REAL tech and a REAL dealer and BEWARE the SHEET on the internet.
even though we all know if its on the internet you can bank on it.

the HORN and the TACH share nothing other than an engine ground someplace and a 12V+ supply.
throw the tach in the EPA approved dump site and the horn still works.
toss the horn AND the tach in the same site and RPM reduction still works.