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Home >> Mercedes Benz >> 1973 >> 280 >> Repair and Diagnosis >> Engine Performance >> Ignition System >> MERCEDES-BENZ 280 & 280C Engine Modification >> Testing >> Checking RPM Switch

Checking RPM Switch

CAUTION: Use only voltmeter for checking electronic RPM switch. Use of a test light may destroy switch.

Disconnect plug of ignition switch-over valve and connect voltmeter. Voltmeter should indicate 13 volts above about 2000 RPM and return to zero when engine speed drops below about 1800 RPM. If no voltage is indicated, remove plug from 12 prong relay box and connect voltmeter to terminals 2 and 3. If 13 volts is indicated above 2000 RPM, replace relay box. If no voltage is measured, replace RPM switch.

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