Postby jimh » Thu May 18, 2023 9:35 am
You should consult the owner's manual for the engine on your boat for the best advice. When asking about an electrical topic related to a particular engine, please identify the engine maker, model, year, and horsepower.
For the ignition key switch to have four positions is a bit unusual. Typically--on older outboard engines--the ignition key switch just has three positions: OFF, RUN, START.
My inference is the ACC position provides 12-Volt power to engine-related accessories. The ON position provides 12-Volt power to the engine and the accessories when the engine is to be running. This position is often identified as the RUN position.
On that basis, if the engine is not running you would not want the engine ignition key switch in the ON position. If you have a modern engine, the engine will typically have microprocessor controllers. When the ignition key switch is in the ON (or RUN) position, those devices in the engine will be powered-on. There is not a particular harm in those devices being powered on, but if the engine is not running there is no need for them to be powered on. Also, the value computed for engine running time may be incremented upward whenever the ignition key switch is in the ON (or RUN) position. Accumulating engine runtime when the engine is not actually running can be misleading, as the basis for certain maintenance intervals may be based on the runtime hours. Also, the microprocessors for the engine will have very expensive replacement costs, so there is little to no value in letting them remain powered-on when the engine is not actually running.
There is no reason to leave the key switch in the ACC position, unless for some reason on your boat there are electrical loads that obtain their 12-Volt power from the ignition key switch accessory circuit. Usually only engine-related accessories like engine instruments would be powered by the ignition key switch accessory circuit.
Without knowing what other electrical loads are powered in the ACC position, I am not sure why you would want to leave the ignition key switch in that position while you were angling. Usually the ignition key switch accessory circuit is protected by a fuse. The typical value of a fuse for the accessory circuit would be 10-Amperes. The total electrical load on the ignition key accessory circuit will be limited to current of less than whatever the fuse value is for your engine. Generally that fuse is under the engine cowling.
Follow-up question to you:
Q2: what electrical devices are being powered by the engine ignition key switch accessory circuit such that you appear to want them to remain operating while you are angling?