280 SL/8 With Automatic Transmission

There are two separate checks to be made on RPM switch, the first for checking fuel shut-off solenoid and the second for checking ignition changeover.

1. Checking Shifting Point 1250-1450 RPM (Shut-Off Solenoid)

   Bridge connecting terminals on idling speed switch. Start engine, remove connector from starter lock and backup light switch and connect terminal 5 to terminal 6. Remove connector from operating current relay and connect voltmeter to terminal 4 and to ground. Increase engine speed, above 1200 RPM voltmeter should indicate approximately 13 volts. Below 1000 RPM voltmeter should indicate O volts.

   Fig 1: 280 SL/8 (Manual Transmission)

   Courtesy of MERCEDES-BENZ USA
2. Checking Shifting Point 2200-2400 RPM (Ignition Changeover)

   Remove connector from two-way valve and connect voltmeter. Start engine and increase speed, above 2400 RPM voltmeter should indicate approximately 13 volts. Below 2200 RPM voltmeter should indicate 0 volts.

Connect test lamp to brown/white wire side of idling speed switch, connect other end of test lamp to ground. Test lamp should light up when ignition is turned on. Test light should go out when throttle linkage is actuated.

Remove connector from relay box and connect test tamp to terminals 8 and 1. Drive vehicle at approximately 25 MPH with selector lever in position 4, release accelerator pedal and allow vehicle to decelerate. Test lamp should light up when shifting back to 2nd. gear (approximately 11 MPH).

Fig 1: Oil Pressure Switch, 280 SE/8 & 300 SEL With Automatic Transmission

Courtesy of MERCEDES-BENZ USA

Connect tachometer, connect test lamp to shut-off solenoid and to ground. At approximately 31 MPH, with selector lever in position 4, test lamp should not light up. Release accelerator pedal (decelerate), test lamp should light up until engine speed drops to approximately 1250 RPM.