'94 merc 75HP overheat alarm

[Huntnfish08]

My overheat alarm is squelching while running and when not running but having key in the on position. Trying to figure out the cause. Here's what I've noticed.

1. Tell tale squirts water at all times. Same temp, figured by feel of hand, as intake water.
2. Compression test has all three cylinders at 120 psi.
3. I have no temp gauge in the boat and where a temp sending unit should be it's got a brass plug.
4. I've got a tan/blue loose wire. Guessing it would hook to temp sending unit. Also two wires that don't connect to anything from engine harness. Dark brown/White stripe and a tan wire.
5. Oil injection tank is full and was replaced last summer.
6. I've ruled out a sticky thermostat or bad impeller based on alarm sounding while not running and cold. I'm sure they are due to be replaced.
7. I heard disconnecting gray wires may stop alarm and rule out temp sensor. Disconnecting gray wires still gives continuous alarm.

I'm at a loss. Wondering if it is a faulty temp sensor or faulty alarm horn. Or something different. Any ideas?

Adam

 

[Ride.race.live]

im going through the same ordeal at the moment with my 92 75 merc. same set up no temp gauge ect...

I know the steady alarm is in regards to the over heat alarm and from all the reading I did the tan wire is tied into the temp sensor. Pretty straight forward to follow non the less.

Looking at my motor I dont have any "unhooked" wires except for the 2 blue wires as I deleted my oil injection but the oil is a beeping alarm anyways from what I read.

My alarm is actually a little intermittent as it will sound off when driving around but will still sound off after the motor is shut down too.


So the way I see it you have and or..... more so either the module or alarm.

A failed sensor
A failed Alarm module
A failed alarm horn

 

[Ride.race.live]

Here's a little write up I came across online that seems pretty helpful and basic

[FONT=Verdana, Arial]To test for the first case, locate the temperature sensor and disconnect it from the alarm system. If this quiets the alarm, then the sensor is bad. If this does not quiet the alarm, look for other alarm sensors and disconnect them individually, check to see if they quiet the alarm. If you find that disconnecting a sensor will quiet the alarm, then it is likely that the problem is localized to that sensor.[/FONT] [FONT=Verdana, Arial]If the alarm persists even with sensors disconnected, the alarm may be coming from the alarm module itself. Locate the alarm sounder. Disconnect the alarm module input lead from the sensor. If this quiets the alarm, then the alarm sounder is working properly and the alarm is being generated in the alarm module. Service or replace the alarm module. If the alarm persists with the alarm module disconnected from the alarm sounder, then the alarm sounder has malfunctioned. Service or replace the alarm sounder.[/FONT]