water temp gauge


New Member
Question: Wiring connections for newly added water temp and oil pressure gauges.

Had a overheating problem on my 2014 Mercury 90hp 4 stroke outboard that I diagnosed as a
stuck thermostat and fixed!

In the process of troubleshooting the overheating problem I discovered 2 sender wires
that were not connected in my steering console. 1 tan labeled water temp and 1 blue
labeled oil pressure. When I had this engine installed on my boat, new by a Mercury Dealer,
I did not have a water temperature gauge or an oil pressure gauge, so they left them unconnected.
The engine has a water temp sensor 885342002 and an oil pressure sensor 897447002 installed
on the engine starboard side, near the oil filter. See attachments.

So I thought this would be a good time to install these gauges to monitor engine temp and oil pressure!
I "assumed" that these sender wires were connected to the engine sensors!
Gauges are hooked up but are not responding. I found 2 capped wires on the starboard side of the
engine (see attachments) 1 tan and 1 blue. I have not check yet if these wires are the same wires
in the console. There are 2 wires coming out of each engine sensor and plugged into connectors.

Question: If these capped wires in the engine are the same wires that are in the console,
where do I connect them to in the engine wiring harness?
I would think 1 wire from the sensor is connected to the Guardian safety system and 1 wire would
go to a gauge sender connection. The sensor body is grounded to the block via the threads.
Do I have to install extra engine sensors????


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Fun Times

Active Member
Hi there, @dpolega112 , welcome to endless boating forums.:)

Are you still working on this?

What is your engine serial number and is the engine Fuel Injected or carbureted?

Do you have a digital display type gauge that reads digital numbers or a needle type gauge?

Those sensors that are plugged in appear to be a digital read sensor,,,,The other wires ought to be for an Analog type gauge.

Depending on your gauge type/design, you may have to change sensor type/design as there are Analog and Digital read sensors.


New Member
Thanks for the reply!
Still working on it.

Purchased new: 05/29/2014
90 hp Mercury 90EXLPT4S
MODEL: 1F90423ED
Engine type: fuel injected
Installed two new Faria "analog" gauges, water temp and oil pressure "after" I found these unconnect sender wires in console.
Needle (analog) type gauges, not digital.
I will research Analog and Digital sensors!
I see a brass plug at the base of the oil sensor connection (see attached oil sensor picture.)
If you are correct, adding a Analog oil sensor here and wiring it to the capped wire is the solution.
I first have to confirm that the wires I connected to the gauge sender terminals are the same wires that are capped in the engine!
I "assumed" too much when I installed these 2 gauges!
Have to find a place to add a Analog water temp sensor. See attachment for digital? water temp sensor that is installed in engine now.
This digital sensor looks like it's plug into a port that's into the "interior" water jacket.
I have seen videos of water temp sensors that are just flush with the "exterior" of the head and read external heat temperature???
Thanks for the advice! I appreciate it!


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Fun Times

Active Member
Thanks @dpolega112 for the engine confirmation as it helps gets you closer to a finished goal.

With knowing what engine type you truly have, 'Another option to look into would be using an Analog Gauge Interface Kit like I believe part number 892486K08 may work which allows the conversion of a digital sensor signal (your sensors installed now) to an analog signal so your new gauges can work.

Or get a digital type gauge unit as they have several types now including VesselView which can be read off of your I-phone,etc. and there might already be a smartcraft type plug under the helm for plug and play to the engine sensors from factory.

Also those digital sensors are what your ECM is reading to know how the engine is doing...You wouldn't be able to remove them or the engine/ECM won't allow the engine to operate correctly...Not sure if there are other places to install other sensors but maybe if those capped wires are truly for analog type sensors.


New Member
Ordered a Mercury service manual specific to my engine.
Wiring schematic confirmed that the wires I connected to the gauge sender terminals are the same wires that are capped in the engine!
Tan wire: "Analog" block coolant temperature gauge.
Blue wire: "Analog" oil pressure gauge.
You were correct, these newer efi engines are all digital.
I'm going to hold off on the Analog interface kit.
I'm going to try and find a place for an Analog water and oil sensor on my engine.
Need to find the Analog sensors too.
Getting closer!
Thanks for the advice! I appreciate it!

Fun Times

Active Member
Aright then @dpolega112 , with knowing that, lets pretend for a few minutes that your engine was Carbureted to maybe help narrow down an alternative starting point....

....Typically the non EFI's analog outboards don't utilizes oil psi gauges and it's about 50/50 of use on the engine temp gauges....
....As because without customer input at time of sale or service of wanting anything installed, if anything's installed at all It may be more common to see either an "indicator light" turn on when the temp gets to hot or oil psi to low and/or sometimes maybe a "warning horn sounding device" as that is an option (too) on some engine models at the boat manufacturers/and/or selling dealers discretion....The warning horn is more common than the light though as the horn would be more from Mercury incorporated into some components and the light "might" be an add-on like just mentioned.

To sound the warning horn or turn on the light or both, The Carbureted engines would use what is called an Oil Switch that opens or closes to ground when out of ohms resistance range...Plus they have an THERMO-SENSOR 804295T That works about the same for the temperature.

The oil switch and T/S would look like these ones, for the carbed engines, https://www.ebay.com/sch/i.html?_fr...0&LH_TitleDesc=0&_osacat=0&_odkw=79-895288A03


The outboards also tend to run Water Pressure (2-30 PSI) gauges Merc kit part number 79-895288A03, https://www.ebay.com/sch/i.html?_fr...esc=0&_osacat=0&_odkw=Mercruiser+79-895288A03
..., Mentioned here in Accessories

Pages 2D-8 - 10 of the following 90-HP carbureted engine service manual would show the temp gauge, warning horn sound display and indicator light wiring diagram connections as possible guides to further your thoughts as a plan of other actions outside of the box of your EFI engine, http://boatinfo.no/lib/mercury/manuals/75-90.html#/154

Now with all that analog carbureted version vs digital fuel injected sensors differences of use laid out on the table, You'd have to come up figuring out how to TEE Or Y into the existing digital sensors as you'd have to keep them so the EFI runs normal.

So with that thought in mind one thought would drift over into the Mercruiser Stern drive EFI's as they utilized both analog and digital sensors so you could use analog gauges while the ECM reads the Digital sensors..., Here's an example of what they were able to do on the stern drive engine models, https://www.nlamarine.com/products/...il-pressure-sender-815425t?variant=1211484268

Merc Oil pressure sender 815425T is the big one on top
See the source image

For safe keeping, here's your 90-H.P EFI engine parts catalog https://www.mercruiserparts.com/75-efi-4-stroke-1b366823-thru-2b0949
And here would of been your 90-H.P carbureted version parts catalog, https://www.mercruiserparts.com/90-4-stroke-0t801000-thru-1b226999

Again, Just helping to think outside of normal but it may be just easier to either find an digital type gauge/s or even mercury marine vessel-view which would show all your engine readings you want right there on your mobile phone, https://www.mercurymarine.com/en/us/gauges-and-controls/gauges-displays/vesselview-mobile/ ;)


New Member
Thanks for the reply!
Contacted Faria about compatible sensors for my Analog gauges.
They suggested attached sensors.
In my new manual I'm finding a lot of M10x1.5 port plugs so I will probably need attached reducer.
I am not going to interfere or disrupt digital sensors that are installed unless it's by a tee.
You gave me a lot think about.
Perhaps it would be easier to pitch the new gauges! HA HA!
Thanks for the advice! I appreciate it!


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