In my 1980 Fiberform, I have no power to any accessories or to my ignition, and my battery seems to have a full charge.
Check battery connections. Check voltage at fuse panel. Should have same voltage as battery. If voltage is present turn on any switch, if voltage goes away with a load follow the no voltage procedure but leave the switch on while testing.
If no voltage, check for any fuses or circuit breakers in the supply wires. Still no voltage: connect voltmeter red lead to positive at battery, black voltmeter lead to negative at fuse panel. Voltage OK problem is with positive supply to panel. If no voltage connect meter red lead to positive at fuse panel, meter black lead to negative at battery. Voltage OK problem is with the negative supply to panel.
If fuse panel is supplied voltage from the ignition switch start the voltage tests at the ignition switch.
Sometimes the positive and negative supply for the fuse panel are connected at the engine. Usually the positive at the starter solenoid, if so use that source instead of the positive battery post. Voltage must be traced from the root source to the load. Both positive and negative must be isolated and verified separately. Without one, positive or negative, there will be no voltage at the load. The load being whatever needs voltage applied to function, (light, pump, etc.)
If there is a corroded connection or wire it is possible for voltage to pass through the corrosion with no load. When a load is applied more amperage is required. The corrosion is not a good enough conductor to carry the required amperage and the voltage goes away. This corrosion can be at a terminal connection, (wire to switch, battery cable to battery lug, battery lug to battery post, etc.), internally in a switch, wire, fuse or circuit breaker. It is possible for a wire to appear to be in good condition. The outer insulation can be intact while the inner conductor is corroded, sometimes turned to green powder. This is why marine grade wire is more expensive than standard wire. Marine grade wire is tinned copper, copper conductor electro coated with tin to resist corrosion.
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