why two wires from temp sender on 470?

I have a 470 mercruiser s/n: C658976 and want to change the temperature sender and gauge. There is only one terminal on the sender so that leads me to believe the sender uses the block as ground (non-floating). There are two wires connected to the sender terminal. I assume one goes to the gauge but where does the other one go? They appear to be tan in colour; one has a blue stripe. They both disapear in the harness and I would like to know where the "other" wire goes.

Thanks

Luc

Re: why two wires from temp sender on 470?

According to the wiring diagrams the tan/blue wire is for a audio warning system, and also connects to the oil pressure sensor. The tan wire goes to the gauge. Here in the manual: http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/174

Re: why two wires from temp sender on 470?


tan/blue is the alarm sensor not the water temp sender

Re: why two wires from temp sender on 470?

Wow, what a resource! Thank-you.

So, from looking at the diagrams, what I was looking at with the 2 wires connected to it was the water temp heat switch (diagram page 4E-2). The water temp sender is shown on diagram page 4E-7.

Are these 2 separate switches/senders?

The "switch" I found was on the underside of what appears to be the exhaust man.

At the risk of sounding like a dumb dumb, where should the temp sender be?

Thanks again.

Re: why two wires from temp sender on 470?

It sounds like you have a combination sender/switch there. I didn't even know there was such a thing.
The tan wire is for the gauge, and the tan/blue is for alarm.
Does your gauge and alarm both work?
Any 2 terminal sender or switch I have seen is either one or the other and the second wire is a ground.

Re: why two wires from temp sender on 470?

I don't know if the alarm works or not. BTW, I just got the boat.

The gauge appears to work but it's kind of a dummy gauge with knotches and a red line. I bought a new Faria gauge with numerical graduations and a sender.

My reason for wanting to change them is when I went to test drive the boat, the gauge seemed to read awfully close to red line. I had a mechanic check this out and he used an infra red gun on the block and various parts of the motor and he felt all was good. He recommended I change at the sender and gauge.

On the diagrams you guys referenced me to, there appears to be as I mentioned (diagram page 4E-2) , a water temperature heat switch with two wires and also a separate sender with one wire. I can't seem to locate this sender.

Also, I quoted my s/n wrong. That was the original motor. The boat had a rebuilt motor put in this spring at a dealership. I thought it was the original motor that was rebuilt but when I checked the tag this evening it read: A 452410. Don't know if this makes a huge difference or not.

Thanks for your help