1998 Johnson Evinrude "EC" 90, 115 SPL Service Manual, P/N 520209, Page 240Get this manual
Running Test, Alternator Output NoteDisconnect battery cables before proceeding with this check1Remove the rectifier red lead from the terminal board or the rectifierregulator red lead from the battery side of the starter solenoid2Wire 0-40 amp ammeter in series with the rectifier red lead and the wiring harness red lead or in series with the rectifier regulator red lead and the battery side of the starter solenoid
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&Guard against any red wire, its terminals, or the ammeter
3The engine's battery should not be fully charged when beginning this testConnect the battery cables and run the engine in test tankRefer to the output curves to determine the correct output-to-RPM ratio for your engine