RPM Switch
On 220 models, disconnect 2 prong plug on vacuum control valve and connect voltmeter. On 280 and 280C models, disconnect plug from 8 prong relay box and connect voltmeter to terminals 1 and 3.
CAUTION:
Do not use a test light as this may destroy RPM switch.
On 220 models, voltmeter should read 13 volts up to about 3600 RPM and should drop to zero above 3600 RPM. On 280 and 280C models, voltmeter should read zero up to about 3200 RPM. Beyond 3200 RPM, reading should be 13 volts. With RPM decreasing, reading should return to zero at 2800 RPM.