1978 Johnson 175, 200, 235 HP Outboard Service Manual, Page 159Get this manual
ALTERNATOR OUTPUT CHECK STEPaDisconnect the red and red purple stripe leads from terminal block #5Connect to 15 amp ammeter between the two leadsConnect the red purple lead from the rectifier to the "G" side of the ammeter and the other red lead to the "B" side of the ammeterbRun the engine up to approximately 4500 rpmThe ammeter should show full charge (approximately 10 amps) 3Ammeter 4Battery
1Starter solenoid 2To accessories
cReconnect the red and red purple leads to terminal block number 5dReconnect the red and redpurple leads to terminal block number 5
AMMETER FROM RECTIFIER REDPURPLE FROM MOTOR CABLE RED
RECTIFIER CHECK STEPaCAUTION: Shut off engine and disconnect battery before checkingrectifierUse ohmmeterHigh ohm scalebDisconnect rectifier leadscConnect one ohmmeter probe to common engine ground, other probe to one yellow leaddNote readingreverse probesnote readingeReading on one check, no reading (infinity) on other checkdiode okfRepeat test using yellowgray rectifier lead and same values