1990 Johnson Evinrude "ES" 60 thru 70 Service Manual, P/N 507873, Page 115Get this manual
Blocking DiodeElectric Models
If the S.L.OWwarning 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 leadrJl 3Calibrate ohmmeter on Rx100 scale and connect between tan lead and engine harness tan pin Note reading4Reverse meter connections or press "polarity" buttonNote reading very high reading00in one direction and low reading in the other direction indicates diode is good5Replace engine harness blocking diode if your test results vary6Complete all circuits disconnected during this test