Mercury Mariner V-250 V-275 Outboard Service Shop Manual 1990, Page 51Get this manual
BRUSHES Testing Positive Brushes and Terminal Set hmmeter to (A scale)Connect mete leads between positive brushesMeter must indicate full con in uity or zero resistance If resistance is indicated, check lead to brush and lead to positive term inal solder connect ionIf con nect ion can not be repaired, brushes must be replaced
Testing Negative Brushes for Ground (Bosch) Set oh mmeter to (A scale )Place one lead of the ohmmete on the negative brush and the other lead on the end cap (bare metal )If the meter indicates NO continu ity, replace the negative bru shRepeat this procedure on the other negative brush