Mercury Optimax Warning Horn wiring

[Capt.Will]

Engine: 2008 Mercury Optimax 150hp.

Over the winter I installed a Smartcraft tachometer for this boat/engine. Unfortunately the manual is extremely limiting on the warning horn installation. The horn simply connects to the Purple and Tan wires from the Smartcraft wiring from engine to gauge.

Issue: No horn beep at start up. After a couple seconds the gauge reads "alarm" and tells me that there is no warning horn. Engine runs fine other than that.

I removed the warning horn and tested it with a 12volt source: OK.

Possible: Could it be that the 2008 Optimax does not offer this warning signal through this Smartcraft wiring harness?

I am finding zero wiring diagrams online for this warning horn.

 

[Capt.Will]

Problem Solved: After viewing several wiring diagrams including the service manual for the Optimax 150. It does reveal a tan/blue wire from the engine leading to the helm that says its for an (Optional) visual warning light.

I found this wire and hooked the horn to it. Purple wire from horn to positive battery lead. Tan/blue wire from horn to the Tan/blue wire to engine. It worked. Got a single beep as key it was turned on and no warning/alarm from the Smartcraft gauge.

I am guessing that the engine computer now senses there is a horn in the circuit and is not firing an error to the Smartcraft gauge.

FYI in the future for anyone searching a similar issue.