Mercury Mariner V-250 V-275 Outboard Service Shop Manual 1990, Page 43Get this manual
2Connect an AC voltmeter to the two YEL LOW lead te rm inals on the regulator terminal blockIf the AC vol tage at idle above is reater than 16 vac, he regulator is defectiveNOT E: he ta cho meter signa is provided by th regulatorIt is possible to still have an acc urate tachometer signal with defective regulatorREGULATION VOLTAGE CHECK NOTE: Battery must be fully charged before testing reg ulation voltageA low battery ill not allow an accurate reading of regulation voltage 1Turn on all electrical accessories and rank engi ne fo 20 seconds with the ignition lanyard switch turned off This will discha rge battery slightly Incorporating Ballery Isolator with V-6 15 40 Amp Charging System
A battery isolator will allow the charg ing system to ch arge both the sta rting battery and an auxiliary battery at the same ti me whi le preventing accessor ies, connected to the auxil iary battery, from draw ing power from the cranking battery 1Install the isolator as presc ribed by the manufacture r
2Locate the stud terminal bl ock on the top rear f