1986+ Mercury 6/8/9.9/10/15HP 2-stroke Factory Service Manual, Page 75Get this manual
CHARGING AND STARTING SYSTEM
9Connect GRAY, YELLOW, and YELLOWBLACK tachometer module leads to engine harness10Measure resistanceMETER TEST LEADS RED BLACK OR GROUND BLACK 1-3M Mega Oh Ohms GRAY TACHOMETER MODULE LEADS METER SCALE READING (W)
11Connect the multi-meter RED lead to the YELLOW tachometer module wireConnect the BLACK multi-meter lead to engine ground or to the BLACK tachometer module bullet connectorMETER TEST LEADS RED YELLOW BLACK 5.5Oh Ohms BLACK OR GROUND TACHOMETER MODULE LEADS METER SCALE READING (W)