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

**VkingMike** · 06-13-2023, 10:06 AM

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

**Aaronhl** · 06-13-2023, 11:18 AM

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

**VkingMike** · 06-13-2023, 11:56 AM

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** · 06-13-2023, 01:46 PM

Originally Posted by Aaronhl

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** · 06-13-2023, 03:28 PM

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?

**OnPad** · 06-13-2023, 05:59 PM

That's what you get fer reading the directions!

**derekfl** · 06-13-2023, 07:44 PM

Try grounding the wire that connects to the sensor.

**Jim Speros** · 06-13-2023, 08:27 PM

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** · 06-13-2023, 09:55 PM

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...................................

**97mirage** · 06-14-2023, 11:42 AM

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** · 06-14-2023, 12:21 PM

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** · 06-14-2023, 06:45 PM

Originally Posted by 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....

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** · 06-14-2023, 07:09 PM

Originally Posted by Aaronhl

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??

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