Merc 280 temp gauge & warning horn questions

[ModVP501]

I bought a Merc 280 (2.5L EFI), which came without a wiring harness and gauges. Seems to run fine: 10 PSI at 5000 rpm and 12-14 PSI at 7000 rpm. I do not have a warning horn or temp gauge hooked up. Need to know if the motor has a temp gauge sensor and what color the trigger wire is for that? Also, does it have an overheat horn sender and what color is the wire for that? I do have a temp gauge and a warning horn that I would like to hook up.



What should be the proper running temperature for this motor? At what temperature should the warning horn sound?

[h2oskiier30]

Temp gauge wire is tan. If there is a sensor, it will be connected to the port side head, between #2 and #4 sparkplug.

[laglass69]

Temp gauge wire is tan. If there is a sensor, it will be connected to the port side head, between #2 and #4 sparkplug.

This is correct. 280s came with a head temp sensor/horn sender on one cylinder head. The tan wire from that plugs into the tan wire on the harness and the horn is in the control box if you have a merc box i think, somebody correct me if im wrong. My 280 runs around 140deg idling and between 155-165deg wide open. I think the horn beeps somewhere around 180deg.