1985 Mercury Outboard V-300 V-3.4L Shop Service Manual, Page 206Get this manual
ELECTRICAL SYSTEM TROUBLESHOOTING GENERAL CHECKS
Before troubleshoot ing the Power Trim elect rical system, check the fo llowing: 1Check for disconnected wires2Make certain ll connections are light and corrosion free3Check that plug-in connectors are fully engaged4Make certain battery is full chargedRefer to the preceding three wiring diagrams for connection points when troubleshooting the electrical system(Connection points are specified by number
Troubleshooting the "Trailer" Circuit (When "Up" Circuit Is OK)
Use an Ohmmeter (Rscale) and check continuity of blue-white
wi re between Point 10 onUp" solenoid and trailer buttonII no continuity, wire is open
If blue-while wire is O.K disconnect all battery leads from battery and check continuity across trailer bullon terminals with trailer button depressedIf no continuity Is Indicated, trailer bullon is faulty