Oil pressure gauge wiring

[sbs_59]

I'm trying to determine what wire color the signal wire is to an oil pressure gauge for a boat I'm building. The motor is a 1998 mariner bigfoot. 25hp, 4 stroke. The wire coming from the oil pressure switch is light blue and goes to the ECU.
Currently at the motor there are 3 wires with bullet connectors but are capped and were not used. A purple wire, a tan/black stripe, and a tan/white stripe. Would one of these wires be correct for this?

 

[Chris1956]

Purple is ign power to gauges.

Brown/white is trim gauge sender.

Tan/blue is overheat horn.

Not sure what tan/black and tan/white wires are. Tan is generally used for alarm wires. See if you can trace their origins under the motor cowling.

Oil pressure alarms to the ECU are usually on/off switches (AKA idiot lights), not variable resistor type sensors, used for gauges.

Maybe you have an oil pressure gauge sender as well. My guess is that tan/black has a chance to be that wire.

 

[alldodge]

Purple is ignition power 12V
Tan/Blk is overheat light
Tan/Wht is low oil pressure light

 

[sbs_59]

Thanks for the replies. Does this mean that if tan/blk and tan/wht are meant for light indication only, there won't be a signal wire for a gauge as well? If the tan/blk is for an overheat lamp, then according to merc's diagram the tan wire is available for a signal to the temp gauge. I was hoping for the same setup with a signal wire to a pressure gauge as well. I have a separate tan wire with a bullet connector coming out of the 5 pin connector at controller, and another separate tan one at the 8 pin connector. I assume I can use either one as my signal to the temp gauge?

 

[alldodge]

Thanks for the replies. Does this mean that if tan/blk and tan/wht are meant for light indication only,

Yes lights only. so its just a switch connection that the ECM switches a ground ON

If the tan/blk is for an overheat lamp, then according to merc's diagram the tan wire is available for a signal to the temp gauge.

I don't believe that will work. Found a wiring diagram for a Optimax and its labeled "light". Merc colors try very hard to not mix them into doing different things on another motor

I was hoping for the same setup with a signal wire to a pressure gauge as well. I have a separate tan wire with a bullet connector coming out of the 5 pin connector at controller, and another separate tan one at the 8 pin connector. I assume I can use either one as my signal to the temp gauge?

That may work because Merc list Tan as gauge or switch to horn. Unable to say for sure, but attaching a gauge to the lead should not do anything to the ECM.

 

[sbs_59]

Here is what merc tech sent me to use. Shows tan wire to temp gauge. Again, i assume i can use the seperate tan wire coming from the 5 pin connector. This diagram doesnt show the tan wire at the 5 pin...the commander 2000 wiring diagram shows it in detail. I can't see any harm in trying it.
Any idea how I could identify if my motor has a variable sending unit with a lead for a pressure gauge?

 

[alldodge]

If its a switch then when motor is OFF a ohm meter will read zero ohms from center condictor to ground. If its a sensor it will read around 30 ohms to ground.