Mercury Water Temp Gauge

[Norm Magnuson]

I have a 2003 Mercury 75 HP serial # 0T787481 and it doesn’t have the optional water temp gauge. It does have a horn connected to the thermosensor on the engine. I have the kit 12415A for the install and 12415 temp sending unit. I have 3 sets of instructions and they do not match my engine. Thinking outside the box, is it possible to replace the thermosensor with the water temp sending unit, modify the wiring, disconnect the horn and use the same wire up to the water temp gauge? This is an analog gauge. I tested the horn today and above the noise of the engine, water, wind, etc. I wasn’t able to hear the horn. Is it wrong to replace the horn if I can make the plumbing and wiring work with the current setup?
Thanks in advance!

 

[Texasmark]

I have a 2002 115 and on the water jacket covering the rear of the block (encircles the spark plugs) there was an 1/8" NPT male brass plug. I found a temp sender and dash gauge and installed them. Temp sender works great and tells me what i want to know about block temperature. When going slow, the temp rises to the temperature of the thermostat...120F When I get on plane and the popoff valve opens, the temp drops to surface ambient temp.

I think I recollect, many years ago that I wanted to know the block temp on my current engine at that time and there was no access point. I may have drilled and tapped a hole in the water jacket cover and installed a sensor and dash gauge. Had I not done that, in short did I remember correctly, I was happy when I decided to have one on my current engine and lo and behold I see the brass pipe plug near the top of the water jacket cover meaning I didn't have to make a hole.

The OT monitor which switches at about 195F to sound the alarm, is in the lower left corner of that cover with a tan wire going to the external wiring harness and I didn't touch it.

 

[Norm Magnuson]

I have a 2003 Mercury 75 HP serial # 0T787481 and it doesn’t have the optional water temp gauge. It does have a horn connected to the thermosensor on the engine. I have the kit 12415A for the install and 12415 temp sending unit. I have 3 sets of instructions and they do not match my engine. Thinking outside the box, is it possible to replace the thermosensor with the water temp sending unit, modify the wiring, disconnect the horn and use the same wire up to the water temp gauge? This is an analog gauge. I tested the horn today and above the noise of the engine, water, wind, etc. I wasn’t able to hear the horn. Is it wrong to replace the horn if I can make the plumbing and wiring work with the current setup?
Thanks in advance!

Thank you for the information. Yesterday I removed the plastic cover over the spark plugs and the two engine anoles were there but I didn’t see nor was I looking for a brass plug. With the age of the engine I ordered new engine block plugs so when they come in I’ll look for the brass plug or any other possible location. Thanks for the response and possibility’s.