1993 Johnson Evinrude "ET" 40 thru 55 Service Manual, P/N 508283, Page 293Get this manual
Rectifier Ohmmeter TestsAmp Models Disconnect battery cables before proceeding with this check
[!] 1Disconnect all rectifier leads from the terminal board2Calibrate ohmmeter on appropriate scaleConnect one lead to clean engine groundConnect the other lead to the rectifier yellowgray leadNote the readingReverse the ohmmeter connections, or press the "reverse polarity" button, and note the reading high reading in one direction and low reading in the other direction indicates the diode is OK Two high readings or two low readings indicates the diode is damaged