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Cruise Control Switch and Speed Sensor Test

Please note that these ideas and procedures are for someone who has the time, inclination and technical ability to understand and follow them. There are other alternatives. We can generally tell you, over the phone or by email, what is wrong with your system if you let us know what the symptoms are. Or, naturally, you can have your favorite local qualified mechanic perform the work. Please do not hesitate to email or call us if you have questions or concerns.

- The Switch is the lever on the near the turn signal switch on the steering column.

- The Speed Sensor is either on or in the speedometer, or inline with the speedometer cable.

- Performing this test along with Amplifier Pre-installation "Actuator and Wiring Check" (Mercedes Benz) will test the system as adequately as using the Mercedes Benz Cruise Control Test Fixture.

- Good results on both tests together do not absolutely assure proper operation of the Cruise Control System because the Cruise Control Amplifier cannot be tested in the vehicle. Without a special test setup there is no way to evaluate the Amplifier. Consequently to test the System in the field under normal road conditions the only way is to use known-good Amplifier and Actuator.

These tests are performed with the ignition switch on and are measured at the Amplifier.

#### A) Switch Test (meter common to ground)

Pin 1 | BV | (BV = battery voltage: somewhere between 12.5 and 13.8 Vdc)
Pin 2 | Decel/Set | 0 Vdc initially - goes to BV for Decel/Set
Pin 3 | On/Off | BV initially - goes to 0 V for Off
Pin 4 | Accel/Set | 0 Vdc initially - goes to BV for Accel/Set
Pin 6 | Resume | 0 Vdc initially - goes to BV for Resume
Pin 8 | Brake Disengage | MUST BE 0 Vdc for Cruise System to work - goes to BV when you step on the brake.

The system gets a critical ground through the brake light bulb filaments. If both bulbs are burned out or there is not proper ground here the system will not work. This is the mechanism for canceling the Cruise when you step on the brake: this pin goes from ground to plus voltage and loses a ground which is necessary for the stem to stay engaged.

Pin 12 | Ground
Pin 14 | Ground (some cars have no ground here; the system will work without it)

#### B) Speed Sensor Test (meter common to ground)

This test must be performed with the rear wheels turning. Please have two qualified people present at all times.

Pin 11 | Speed Sensor | loaded (with the amplifier plugged in) must be at least 2.0 Vrms at 25 mph.

The amplifier actually measures the frequency of this signal. At 60 mph the frequency should be 131 Hz.

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General Development Laboratories
3041 Sandalwood Avenue
Morro Bay, CA 93442
805 772-5127