90 TLRZ Alarm and Guage Issue

[caritobito]

Hello. Just got my first boat. Has a 2001 Yamaha 90Z on the back. Taken it out a few times with no issues until recently and hoping someone can offer some advice on what I should replace.

Last time I took it out, the tach started going crazy. Would go to zero then normal and not work a while then go too high etc etc. I looked up under the console and none of the wires are loose. All the guages appear to be original.

I also noticed that my voltage guage appears to be stuck in the maxed out position even when off. Prob bad guage.

Anyhow I pulled off the cover when I got home. The only thing I saw is on right hand side of the motor from standing behind it, there are two plugs laying there not plugged into each other.
One's a female with 3 wires. (grey, pink, and black) There is a male plug laying there with 2 wires (green, and green w/red stripe). I had read that the grey is normally a tach wire. I figured there was no way the plug came undone, because the tach has been working fine until I pounded on a few waves.

I plugged in the two plugs and as soon as I turn on the key with the motor off, an alarm sounds on the console. Its my understanding that the motor has a low oil alarm and a high temp alarm.

How can I diagnose what is wrong and why the alarm comes on? Seems weird that one plug has two wires and one three. Id like to have it plugged in like its supposed to and not alarm. Also, does the tach connect to the voltage regulator or something called a sender switch? I can buy whatever, just dont want to buy more then I need. I will also prob go ahead and get a new voltage guage and tach guage also.

I have no service papers on the motor. But Ive recently changed the water pump, plugs, fuel separator, lower boot oil, and propellor seals.

Thanks!

[caritobito]

Well it looks like the wires go to the low oil sending unit. It appears the grey wire goes to the green and the green/red stripe goes to oil unit.

I traced the grey wire back and it goes a few inches to something that looks like a capacitor. From here it connects to a pinkish colored wire that runs up and connects to another wire to some little round thing that is screwed into something at the top rear of the motor above the top cylinder.

So. Thinking I need a new low oil sender but I still dont understand about the tach. How do I figure out why its acting erratic? I thought it would be the grey wire, but if thats the case, how was it working with the plug undone?

[boats.net]

Un plug those two wires on engine and alarm will not sound, they should not be connected to each other, those are for the digital type Yamaha gauges and not used on aftermarket analog gauges. Probably need to replace tach and voltmeter.

[caritobito]

Thanks for the reply. I will order both a new voltage guage and analog tach today since they are so old and leave those two plugs undone.

Hopfully that is all it needs. Trying to learn as much as I can.

Thanks.