Mercury 35/40HP 2 Cylinder Outboards Service Manual PN 90-42794--1, Page 368Get this manual
Horn Does Not Sound Low Oil Warning (Beeping Tone) When Oil Level Is Below 114 Full TEST 1: Turn key switch toOFF" position then install jumper wire between terminals of 2-pin connectorThen turn key switch toON" position
Horn does not sound ,Horn soundsGo to TEST 21
Go to "Horn does not sound self-test beep when key switch is turned ON" and perform troubleshooting steps outlined
Check for continuity between both pins in tank receptacle, first with AutoBlend upright then with AutoBlend inverted
No continuity present with AutoBlend in either position
Continuity present with AutoBlend invertedReplace internal oil filterGo to "Horn does not sound self-test beep when key switch is turned ON"
Horn Has Weak Sound
Check forTEST 1: connector.presence of battery voltage (9V DC minimum) at pin #1 of 3-pin Key switch must be inON" position