Faulty overheat alarm?

[jessejames556]

I have a 1995 Mercury 75 HP 2 stroke outboard. I believe I may have a faulty overheat alarm sounding, but I wanted to get some opinions first. Also looking for advice on how to change it out or determine if that is really the problem. 

 

The alarm sounds at the ignition by the console. Its a continuous buzz alarm but it changes pitch and volume on occasion, like a bad connection. The alarm sounds even after the boat has been sitting for a week and I turn the key without starting the motor, so I know it isn't overheating at that point. I have ruled out the common issue with the oil reservoir sensor going bad because I disconnected the wires to it after starting my troubleshooting on the alarm. Thoughts? 

[riverbasser]

I believe the alarm sounds by completing the ground circuit so look for a short to ground. I would start at sensor on block and work forward.

[jessejames556]

Okay, any guess on the color of wire? I'll find it otherwise but I am away from my boat right now.

[riverbasser]

Going off memory but I want to say brown. You know where the sensor is right? Should be on the head and easy to see. If not go on a parts website like boats . net and look at the breakdown.

 

Look for the connector and unplug it, if the alarm still sounds it's a wiring issue. If it doesn't it's either a bad sensor or the in the short section of wires coming out of the sensor grounded.

[jessejames556]

Alright, did a little digging and this is what I have figured out thus far. The tan and blue wire connects to the back of the head where the overheat sensor is. This wire runs to around the engine to the side where a plastic cover contains a few different wire connections. After removing the cover, I see the tan/blue stripe wire connects to an apparent grounding screw. Two other wires also connect here. I removed the screw and found a second tan/blue stripe wire running from this screw into rubber conduit that joins several other wires (possibly ends at the throttle console?). The third and final wire ending at this screw is all tan and runs toward the lower portion of the engine where I lose sight of it. 

When I disconnect the tan/blue stripe wire that runs to the overheat sensor and leave the other two wires connected at the screw, I still get the alarm. When I disconnect any of the other two wires from the screw and leave the overheat sensor wire connected, I no longer get the alarm (I also do not get the initial turn key beep at the console when I do this). I disconnected all wires from the screw and touched the tan wire with the tan/blue stripe rubber conduit wire and I get the alarm when they touch. 

 

My knowledge of electrical systems is pretty limited. Any thoughts on this?