1978 Johnson 55 HP Outboards Service Manual, Page 100Get this manual
STARTER SYSTEM VOLTAGE DROP TEST aBy making systematic check from the positive battery terminal, through the starting circuit and back to the negative battery terminal, any component or electrical connection having excessive resistance, thus causing high voltage drop and subsequent hard starting, can be locatedSee belowbDisconnect four wire connector between armature plate and power pack so that engine can be cranked without firingConnect voltmeter and turn ignition switch to START to crank engineBy placing voltmeter leads against battery, solenoid, and starter motor terminals rather than against connecting cable ends, each connection can be tested for high resistance along with componentcClean and retighten, or replace, any connection, cable, or component having greater than specified voltage dropAfter test, reconnect four wire connector between armature plate and power pack
,12 VOLT BATTERY ,
Connect voltmeter positive lead to battery positive postConnect voltmeter negative lead to starter solenoid positive terminalTurn key switch to start to crank engineVoltage reading should not exceed 0.30 voltsSOLENOID SWITCH STARTER MOTOR