Can someone explain to me Water Temperature Switch & Temperature Gauge Sender

[Aaronhl]

On a mid 90s 200 2.5 fishing motor, each cylinder head has a "sensor" bolted to it. How are they wired?

Do I even need a "Water Temp Switch"?

Seems like only the black boxes I removed connected to that, but it does have a tan/BLUE wire going to the terminal block near the starter solenoid, and the diagram connected the tan/BLUE to the 8-pin control cable....not sure what the water temp switch is used for?

I was thinking of removing the "Water Temp Switch" and the terminal block completely.

The "Temp Gauge Sender" I will be wiring straight to the temp gauge with a tan wire/separate from the controls...

?????????????

[Mark Poole ModVP]

The water temp sensors in the cylinder head are overheat activated and make a closed circuit which sets off the overheat horn. If there are wires that run to the ignition boxes then it must have an rpm limiting feature. Typically, a temp gauge sender will simply be installed so that it contacts the cylinder head surface so that it can operate the temp gauge.

[tlwjkw]

it is an efi right? if so there are two sensors that deal with temp... tha one in tha starboard is over temp sensor.. goes ta ground and sets of a continuous buzzer.. tha one on tha port head is a combination temp sensor for tha efi and a sensor for a temp gauge.. two tan/blks go to to tha efi harness... tha single tan is for tha optional temp gauge...............

[Aaronhl]

The water temp sensors in the cylinder head are overheat activated and make a closed circuit which sets off the overheat horn. If there are wires that run to the ignition boxes then it must have an rpm limiting feature. Typically, a temp gauge sender will simply be installed so that it contacts the cylinder head surface so that it can operate the temp gauge.

Thanks for the input Im posting over here in NAMBA dist 11

[Aaronhl]

it is an efi right? if so there are two sensors that deal with temp... tha one in tha starboard is over temp sensor.. goes ta ground and sets of a continuous buzzer.. tha one on tha port head is a combination temp sensor for tha efi and a sensor for a temp gauge.. two tan/blks go to to tha efi harness... tha single tan is for tha optional temp gauge...............

No it's a carb motor - are you saying one sensor controls the alarm and one is for the temp guage?

[tlwjkw]

yes, two completely different circuits.. if its not a efi it may/may not have single sensor on tha port side for tha temp gauge.. early years tha temp gauge was an option so in tha same time period tha motor would not have tha sensor from production on it... you can tell tha difference in tha two sensors by number/color of wires.. over temp (star) is a single tan/blu and temp gauge (port) will have a solid tan and a blk ground...

[Mark Poole ModVP]

Is that your Velocity in your pic? What year is it? I was working there in the early 90's.

[Aaronhl]

Yes I bought it a little over a year go - it's a 2000
You must know Scott McCormick then
I volunteered at his shop new Velocity shop for a few days earlier this year !!

519495

[Mark Poole ModVP]

He bought it from Steve well after I had moved on. Built some cool project boats and race boats back in the day there.

[Aaronhl]

seems like after researching more of the wiring,

the tan wire built into the engine harness connects to the ground tab on the temp warning buzzer,

and the tan wire separate from the engine harness goes to the temp gauge...

Does that sounds right??

[tlwjkw]

if tha two tans arn't designated by a stripe then you may need ta do a continuity test on 'em if they have been fooled with..
this is tha way they should be from production.... tha one on tha starboard head (over temp) should go to a plastic terminal just above tha switch boxes/starter sol.. which it in turn goes into tha motor harness (female end).. tha one coming for tha port head (temp gauge) should have had one half of a "bullet" connector tha will plug into tha other half on tha "boat side" of tha harness..

think this is tha way it supposed ta be but got a lotta dead brain cells at my age............

[Aaronhl]

if tha two tans arn't designated by a stripe then you may need ta do a continuity test on 'em if they have been fooled with..
this is tha way they should be from production.... tha one on tha starboard head (over temp) should go to a plastic terminal just above tha switch boxes/starter sol.. which it in turn goes into tha motor harness (female end).. tha one coming for tha port head (temp gauge) should have had one half of a "bullet" connector tha will plug into tha other half on tha "boat side" of tha harness..

think this is tha way it supposed ta be but got a lotta dead brain cells at my age............

thank you so the tan/blue stripe built into the harness (one of 8 pins) from the terminal block should be connected to the warning horn?
and then the tan only wire that is a bullet connector into the side of the harness should go to the temp gauge?

[Aaronhl]

I have a cut harness the previous owner cut all the wires that plug into the side of the 8 pin harness, I have a completely seperate tan wire, and trim wires, I need to figure out how to wire the warning horn and get the harness plugged into a remote ignition switch

[tlwjkw]

thank you so the tan/blue stripe built into the harness (one of 8 pins) from the terminal block should be connected to the warning horn?
and then the tan only wire that is a bullet connector into the side of the harness should go to the temp gauge?

:thumbsup:

[Aaronhl]

And how do I test that the warning horn is functioning properly (other than overheating my engine !!)

Does it beep when I first turn the key?

[VkingMike]

Key on, Apply ground to the harness side of the 2 post block where the temp sensor and harness meet.

[Aaronhl]

OK So you are saying when the overheat alarm is on the tan/blue wire grounds to the engine block?

[VkingMike]

If my memory serves me correctly, the overheat alarm sensor is a solid tan wire. The tan/blue is for a cylinder head temp gauge ( the kind that only has a C and H no actual numbers. When the engine gets to a certain temps, the sensor grounds the tan wire thereby grounding the buzzer.

[tlwjkw]

OK So you are saying when the overheat alarm is on the tan/blue wire grounds to the engine block?

yes.... if its tha one coming from tha starboard head.. jus ground it at tha terminal that Mike said with key on and you should get a buzzer.. tha warning beeps when you turn tha key on are strictly self test of tha oiler junk.. have nothing ta do with over temp......

[Aaronhl]

How does this from the service manual make any sense - it says starboard head but shows a picture of the port side - And is this the one that controls the TEMP GAUGE or the OVERHEAT ALARM?

https://i.imgur.com/sF0ENaz.png

[OnPad]

That's what you get fer reading the directions!:reddevil:

[derekfl]

Try grounding the wire that connects to the sensor.

[Jim Speros]

I suspect it is not a Mercury manual. It does not even name it correctly. Some after market crap.

Alarm sender is often a black wire. It does not have a bullet connector. It has about an 18 inch lead with a protective sleeve with ring terminal on end. It is mounted under #1 cylinder on stb head.

[tlwjkw]

It is a merc manual but looks like tha nomenclature didn't make it thru QC.... can see why tha confusion!.. tha starboard head is OVER TEMP SENSOR, should have one tan/blue wire with eyelet made up on tha terminal block.. tha port is temp gauge sensor, has two wires, one tan with bullet connector (jus like jim says) and one black.. ALL BLACKS ARE GROUNDS.... jus like we've been sayin' all along...................................:reddevil:

[97mirage]

In looking at the diagram that Aaron posted, I believe that it is showing us the starboard head? The heads are at the rear of the engine, so if you’re looking forward (from the head side), the diagram is showing the starboard (or right) side. If you look at the image from the perspective shown above (from the crankcase side), it appears to be the port (or left side) but we are viewing it backwards in that image. I could be wrong but that might explain the confusion?

[tlwjkw]

tha thing that stands out is its showing BOTH with two wires.............. tha over temp has only one, no ground... tha case of tha sensor serves as a ground....

[Aaronhl]

tha thing that stands out is its showing BOTH with two wires.............. tha over temp has only one, no ground... tha case of tha sensor serves as a ground....

Exactly!!!

So the one with the ground on the port side goes to the TEMP GAUGE
And the one on the starboard side blue/tan WITHOUT ground goes to the warning horn?

Final answer??

[tlwjkw]

Exactly!!!

So the one with the ground on the port side goes to the TEMP GAUGE
And the one on the starboard side blue/tan WITHOUT ground goes to the warning horn?

Final answer??

:thumbsup:... by way of tha term block above tha starter solenoid...

[Aaronhl]

:thumbsup:... by way of tha term block above tha starter solenoid...

OK Thank you gonna try to finish riggin this up in a few days