ELECTRICAL SYSTEM
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• Kohler makes a proprietary Rectifier/Regulator
tester (Kohler Part Number 25 761 20 and the
up-dated version: 25 761 20-S). This tester
works on Kohler regulator / rectifiers and the
company claims it works on similar systems from
other companies. See Figure 7.35.
• Instructions are included with the Kohler tool
(TT480-A)
Testing the charging system
Quick and dirty test: check voltage across the battery
posts using a DMM set to read D.C. voltage with the
engine turned-off. It will read battery voltage, typically
around 12 V. Start the engine and repeat the voltage
measurement. The system voltage should rise, reflect-
ing the out-put of the charging system, typically in the
range of 13.0 - 14.5 V. If the voltage does not rise, or
rises significantly above this threshold, there is a prob-
lem with the charging system that needs to be identi-
fied using more in-depth techniques.
NOTE: If system voltage is beyond roughly 15.7
volts, it is over-charging and there is a problem
with the voltage regulator / rectifier.
To identify a specific charging system problem, isolate
the components of the system and check their perfor-
mance individually.
1. First check the raw AC. Voltage out-put from the
stator. It will be necessary to compare it to the
engine manufacturer’s specified out-put. This
varies from model to model.
1a. With a DMM set to read AC Voltage, con-
nect the probes between ground and one
of the AC wires of the stator.
1b. Leave the regulator-rectifier connected to
the harness.
1c. Start the engine and run it at the RPM
specified by the engine manufacturer.
1d. Read the voltage on the meter.
1e. If the voltage is substantially low, try the
other AC wire.
2. If raw out-put of the running alternator is less
than the manufacturer’s specifications, check
the stator.
2a. With the engine stopped, unplug the stator
lead from the voltage regulator / rectifier.
Figure 7.35
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