150 04 optimax
 

Hi guys I am getting alarms with this outboard... iwas told water in fuel..but when I check the filters there is no water...has anybody had these issues engine... will try an auxiliary fuel tank just to make sure... I just have not seen any water..perhaps bad sensor. Or maybe it is something else... no smart guage just the the 4.four light sensor

I have heard that the sensors will fail and give you a false water when you don't have any or have water and not go off. Not sure on you motor but mine (225 efi) a has the sensor located in the bottom of the water separator filter on the engine. I think opti takes the same filter as the efi. Mercury has 2 different sensor types- a blue one and a black (mine uses the blue). When you buy a new filter it comes with the sensor. I know some people reuse them but I change mine every time I change the filter. I would replace it if you keep having issues. My buddies efi never went off recently when he had issues but his filter was half way full of water. The motor just started acting up. We dumped it out and it was obvious it wasn't gas in the bottom half of it. We changed the filter and it came with a new sensor. I feel like it should of went off long before he got that much water in it.

sensor
 

Are these looking for ground via resistance to ground??

Low oil on the engine mounted oil tank will give the same alarm. It must be filled to the top. Pull the cowling, remove the cap from the engine mounted oil tank, start the engine and it will fill up. Put the cap on when it is full and cycle the key.

Thanks .. I did check that

The sensor can be jumped out by just connecting the two wires together. It needs to see conductivity threw the sensor or a jumper to stay off. Alarm sounds once circuit opens up. Most alarms are this way so you get an alarm when either 1) the sensor reads a problem or 2) there is a fault in the wiring loosing current/voltage, both ways it lets you know there is a issue. You can jump the wires out to see if it has a bad fuel sensor. If it is not the fuel try jumping out the full oil res sensor. I think there may different beep counts of the horn too. Seems like it will beep different pulses to let you know which one it is, On beep is this - two beeps is that- three beeps is something else...

If the opti beeps four times then it should be one of two things 1)water in the fuel or 2)oil level in the oil res is too low / bad float switch in the tank
Mercury has a know issue with the float switches in the tanks as well, many have full tanks but the float sticks and the tanks has to be replaced due to bad float.