2 cycle oil alarm

[gradywhit]

I have a 2000, 250 hp yamaha 2 stroke. The tach shows 1 solid bar, the second bar is flashing and the third bar is not lit. my trim guage does not read the trim position correctly, have oil in both tanks. operated the boat all summer like this, but want to get it fixed.
My thought was one of the oil level tank guages, but not sure which one of if that was it, appreciate any help. Thanks

[boats.net]

If no warning buzzer is coming on and oil transfer from boat oil tank to engine oil tank is working ok then probably have an open circuit in green wire in harness between engine and tach.

[gradywhit]

I disconnected the wiring harness on the sender unit from the tank on the engine and then reconnected it ...buzzer is now going off. how do I test sendering units on both tanks. i also changed both 2-cycle oil filters.
do you know what sendering unit feeds the tach.

[rodbolt17]

neither.
the oil visual indicate is fed via the oil control unit in the ECU based on SW1,SW2 SW3 and SWB switch positions.
SWB is the switch in the remote tank.
wire color is black and black with red tracer.
with switch closed the green or green/white wire from the engine to the tach is grounded.
this leads to a green lamp or a far right bar.
when opened(ungrounded) this illuminates the yellow or center bar and automatic oil transfer is inhibited.
SW1 ,SW2 and SW3 are switchs in the engine tank,float all the way up and the transfer pump is off,float in the middle,SW2 closed, and transfer pump is commanded on,float all the way down,SW3 closed and a second transfer pump on command,far left bar or red lamp,via the green/red wire, RPM reduction and audible alarm.
no alarms,other than yellow lamp or center bar, is associated with SWB.
its a dirt simple system that kicks techs butts.

[gradywhit]

what should i check/replace so my oil bars on the tach stop flashing.

[rodbolt17]

key on engine off.
check continuity from the tach two wire connector green/white to ground.
should be a low ohm value.
if not trace it back.
if it is then most likly the tach has failed internally.