Mercury Mariner Outboard 225 3 Litre Service Manual 1994, Page 46Get this manual
2 Start engine and allow to warm upIncrease engine RPM from idle to 2000Normal voltage output should be 13.515.1 voltsIf voltage reading is greater than normal, replace voltage regulatorIf voltage reading is less than normalfabricate tool from piece of stiff wire to the following specifications:
CURRENT OUTPUT
With engine shut off, install ammeter (capable of reading 60+ amperes) in series between TERM INAL on alternator and POSITIVE (+) terminal of battery20002Start engine and allow to warm upAdvance RPM to
3Insert toolpreviously fabricated for VOLTAGE OUTPUT, through end cover and ground TERMINAL F
5 in(127mm)
Insert bent end of tool through end cover and ground TERM INAL F