A ground side switch is located between the load and ground in a circuit. Inside the ECM there is resistor (load) connected in series to the switch. The ECM measures the available voltage between the resistor and switch. When the switch is open, the ECM reads supply voltage. When the switch is closed, voltage is nearly zero.
The following switches are typically found on the ground side of the circuit:
• TPS Idle Contact (IDL signal) The TPS Idle Contact Switch uses a 12 volt reference voltage from the ECM.
Power Steering Pressure Switch. Overdrive Switch.
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