1991 Johnson/Evinrude EI 60 thru 70 outboards Service Manual, Page 124Get this manual
Blocking DiodeElectric Models
If the 5.L.0Wwarning system is activated when warning horn receives no oil, low oil, or fuel vacuum signal, test engine harness blocking diode1Disconnect engine harness red connector2Disconnect temperature switch tan lead
r:;J 3Calibrate ohmmeter on appropriate scaleConnect between tan lead and engine harness tan pin Note reading4Reverse meter connections or press "polarity" buttonNote reading high reading in one direction and low reading in the other direction indicates the diode is good5Replace engine harness blocking diode if your test results vary6Complete all circuits disconnected during this test