1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 123Get this manual
Low Oil Sensor Test NOTE: Low oil sensor is located in bottom of oil tank1Disconnect low oil sensor leads (tan and black) from terminal block2Using an ohmmeter, perform both tests in chart, followingOil Level in Oil Tank 12 Full to Full Empty Test Leads Between Low Oil Sensor Leads (tan and black) Low Oil Sensor Leads (tan and black) Scale Reading (x) No Continuity (R 1) Continuity (R 1)
With the ignition switch in the "Run" position, electrical current is routed thru the warning horn and supplied to the powerhead temperature sensor, low oil sensor, and warning horn test buttonIf the powerhead overheats, the oil level in the oil tank drops below approximately quart (.95 liter), or the warning horn test button is depressed, the electrical circuit completed, and the warning horn will soundWARNING HORN SYSTEM CHECK
IMPORTANT: Warning horn will sound if powerhead is overheated or if oil level in oil tank has dropped below approximately quart (.95 liter)1Turn ignition key switch to "Run" position2Depress test buttonWarning horn will sound if system is functioning properly3Turn key switch to "Off" position