High Reading; Normal Reading But Corrosion Is Evident; Corrosion On The Entire Sterndrive Unit; Corrosion Problem Developed After Refinishing The Drive Unit, Paint Blistering On Drive Unit - Mercury BRAVO Service Manual

SERVICE MANUAL NUMBER 28

High Reading

Stray current corrosion. If an electrical
current flowing along a metal conductor
leaves the metal for a water path, it will
cause ionization of the metal, and an area
of rapid corrosion.
Poor connection between MerCathode
reference electrode lead (brown) and "R"
terminal on controller.
Faulty MerCathode reference electrode.
Faulty MerCathode controller.

Normal Reading But Corrosion is Evident

CORROSION ON THE ENTIRE STERNDRIVE UNIT

The sterndrive unit is raised so that
the sacrificial anodic trim tab is out of
the water.
CORROSION PROBLEM DEVELOPED AFTER REFINISHING THE DRIVE UNIT
A steel wire brush was used to clean
the aluminum casting. Steel particles
became en-trapped and set up a
small galvanic cell.
PAINT BLISTERING ON DRIVE UNIT
Battery charger, using 110 volt
shore power improperly connected to
the battery.
90-863160 MAY 2000
Cause
Cause
Cause
Cause
CORROSION PROTECTION - ALL MODELS
Special Instructions
Observe the reading while disconnecting
the electrical components one at a time
until you eliminate the high reading.
Correct the course of stray current.
Clean and /or tighten connection. Repair
wiring as required.
Disconnect the reference electrode lead
(brown) from "R" terminal on the controller.
Connect the lead to the positive (+)
terminal of a digital multi-meter (set on
0-2000 millivolt scale). Connect the
negative (–) meter lead to the negative (–)
battery terminal. Note the meter reading;
then, repeat the test using MerCathode
Reference Electrode Tester 76675A1.
Both tools should produce the same
reading. If not, replace the reference
electrode.
Replace the controller.
Special Instructions
Leave the sterndrive unit in the IN/DOWN
position when the boat is moored to
ensure the trim tab is in the water,
providing protection.
Special Instructions
Use only a nylon or bristle brush.
Special Instructions
Ensure the charger is connected
correctly.
Page 7A-21