Re: 1998 Mercury 150 low oil alarm
The tank float on the IN-line motors is the one that the magnet falls off the float, the V-6 motors tank cap is totally different style and do not have the magnet.
The V-6 motor mounted tank MUST BE over-filled, as in loosen the cap with the motor running at an idle to allow oil to transfer from the main tank to the motor tank until it actually starts leaking from over-filling, THEN tighten the cap snugly.
The alarm module is triggered by this cap/switch, it can also be triggered by sensing any difference between the oil pump rotation sensor and the ignition pulse monitored off of one of the ignition coils, usually #4.
Test by disconnecting the oil cap wires, start the motor, does it alarm now?
If no change, reconnect the cap wires and disconnect both the pump rotation sensor and the green ignition wire coming from one of the ignition coils. Start the motor, does it alarm now?