Temp sensor troubleshooting

[Justin_C]

First off, our boat is a 97 Malibu Echelon with the Merc Black Scorpion engine.

 

Our temp guage has never worked since we bought the boat a few years ago and I'd really like to get it working. I tested the guage itself with a multimeter and it seems to work (I can pin it when I give it a little juice). I've also replaced the sensor to no avail.

 

My next step is to check the wiring by wiring it directly. Can someone tell me if I literally just wire it straight to the guage/ground or does the hot side go somewhere before it gets to the guage? Also, any other ideas what could be causing the issue?

[chrislandy]

you will have 12v coming into the gauge, this then earths though the sender.

 

So, check for 12v before the gauge (no power), after the gauge (dodgy gauge or connection) and at the sender (dodgy wire), at the same time, check the earth connections on the back of the gauge (in case it references - connection & resistance to the battery earth connection)

 

if it's the wire, then check the connector where the harness leaves the engine and goes into the boat (mine is at the rear, just above the starter - but may be different on yours)

[Justin_C]

So if I suspect bad wiring and were to rewire it all together, should it be wired through the battery? Meaning the hot wire leave the engine connection, go to the battery, then to the guage and the ground wire go from the connector at the engine right to ground?

[chrislandy]

I don't know how power gets to your dash, but test that first and it will tell you a lot of things depending on the voltage

[fu_man]

Did you ground the gauge to verify it is functional and has power? When you replaced sensor did you use sealant/tape that would interfere with its ground connection?

 

If you think its the wire, use a meter to test continuity on both ends of the the sender wire.

[BraceMaker]

Starting at the temperature sender take the wire off the gauge, key on, touch the wire to the block of the boat. Does the gauge peg?

 

If no put that back together and move on behind the dash, key on ground the sensor to the ground stud, does it peg?

 

The gauge is basically just a power a ground and a sensor wire - the sensor wire is just another ground that has a variable resistor that gets less and less resistive as the temperature goes up.