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Temp sender wiring

G

Gage

New member
Hi all,

did a search and came up empty.

Engine:
1996 2 stroke 4 cylinder 40 hp

question: I'm trying to determine if my motor came with a temp sender I could tie into as I try to install a temp gauge. If so would greatly appreciate your help in determining location and color. My seloc manual is useless.

thanks!
 
There was one on the (factory) electric start models.

It would be located on the (head) water jacket cover, down near the bottom sparkplug.

It should have a tan wire that leads to the location of the main harness, but doesn't go directly into the plug itself. There would be an "extra wire" with a single female style socket that is wrapped in with the main harness that would go up to the controls (on power tilt models there is a couple "extra" single plugs there as well for the up/down etc).

If the sensor is not there you can add one yourself. There are a number of aftermarket temp units on the market (much cheaper than "genuine" merc parts)
 
Thanks graham - there is a tan with blue stripe wire near the spark plug of the top cylinder is this the wire I should trace out?
 
No, that is a temp sensor but not what you are looking for.

There is an overheat warning horn (alarm module) on your motor. That tan/blue goes to a much simpler button type sensor than what you require for a temp gauge.

The sensor on the end of that tan/blue looks like a little watch battery with a lead coming from it. It presses into the block (usually with a grommet style seal). If the temp goes above whatever it built to withstand it simply goes "to ground", completing the alarm circuit and "beeeeeeeeeeeeeep".

The sensor you are looking for should be down at/near the bottom sparkplug and it will have a threaded stud extending from it. Generally the little sensor screws into a threaded hole in the block and then you connect the lead to the (exposed) threaded stud with a nut. It also works on resistance, but it is designed to (drive) the needle on a temp gauge - the other sensor (on the tan/blue) is not...
 
The difference in the two sensors is that if you remove the wire from the OT sensor at the first junction....just pull it apart, it will read open to ground until the engine water gets to about 195 F for most that I am aware of. Then the button Graham mentioned will short the wire to ground, as he said energizing the horn.

The sensor that is designed to operate a temp gauge is an alalog device and the gauge and the sensor are in series across 12v and ground. As the temp of the coolant changes the temperature sensitive resistor in the sensor changes resistance causing the current through the meter to change thus changing the deflection. So to ohm that sensor you would read probably something like 30 to 300 ohms depending on the temp.....definitely not an open nor a short to ground.
Personal comment: Surprised that Merc would put two sensors on an engine of that hp. I have a 90 ELPT and only have the OT, but I do have a 1/8 pipe brass plug in the rear of the head water jacket cover where one could be added.

I looked for a wire Merc might have in the wiring harness for that function in the 75 to 125 inline 3 and 4 cyl engines and found none. Also looked in the Quicksilver Commander remoter control wiring harness and found no wire/color either.

Maybe have to run a separate wire.

HTH,
Mark
 
Texasmark said:
The difference in the two sensors is that if you remove the wire from the OT sensor at the first junction....just pull it apart, it will read open to ground until the engine water gets to about 195 F for most that I am aware of. Then the button Graham mentioned will short the wire to ground, as he said energizing the horn.

The sensor that is designed to operate a temp gauge is an alalog device and the gauge and the sensor are in series across 12v and ground. As the temp of the coolant changes the temperature sensitive resistor in the sensor changes resistance causing the current through the meter to change thus changing the deflection. So to ohm that sensor you would read probably something like 30 to 300 ohms depending on the temp.....definitely not an open nor a short to ground.
Personal comment: Surprised that Merc would put two sensors on an engine of that hp. I have a 90 ELPT and only have the OT, but I do have a 1/8 pipe brass plug in the rear of the head water jacket cover where one could be added.

I looked for a wire Merc might have in the wiring harness for that function in the 75 to 125 inline 3 and 4 cyl engines and found none. Also looked in the Quicksilver Commander remoter control wiring harness and found no wire/color either.

Maybe have to run a separate wire.

HTH,
Mark
Click to expand...

hi mark,

i think you are correct - I can't locate a sensor other than the one mentioned above and I have the same brass plug
 
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