2005 Yamaha F90TR 90HP Outboards Factory Service Manual, Page 199Get this manual
Special service toolsChecking the electrical components
Checking the electrical components
Measuring the peak voltage
Measuring the lower resistance
NOTE: Before troubleshooting the peak voltage, check that all electrical connections are tight and free from corrosion, and that the battery is fully charged to 12 VThe condition of the ignition system can be determined by measuring the peak voltageCranking speed is effected by many factors, such as fouled or weak spark plugs, or weak batteryIf one of these factors is present, the peak voltage will be lower than specificationIn addition, if the peak voltage is lower than specification the engine will not operate properly
When measuring resistance of 10 or less with the digital circuit tester, the correct measurement cannot be obtained due to the internal resistance of the testerTo obtain the correct value, subtract the internal resistance from the displayed measurementNOTE: To obtain the internal resistance of the digital circuit tester, connect both of its probes and check the displayCorrect valuedisplayed measurement internal resistance