Mercury Mercruiser GM V-8 305 CID / 350 CID Engines Service Manual., Page 675Get this manual
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DIAGNOSTICS
PROCEED TO 12 Step 2 Step 3OBD Step 6
TESTING OIL PRESSURE SWITCH
Step Action aDisconnect MEFI or MEFI BLUTAN or MEFI BLU wire from oil pressure switch1bEngine OFF