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89 Subaru justy vehicle speed sensor testing

My Chilton manual says “1. switch the ignition on and check the voltage on VSS terminal 29 of the ECU. 2. The voltage should vary above and below 2 volts with the vehicle moving slowly.”
I think I’ve found the correct wire, but I’m not sure about the testing procedure. Would I unplug the wire harness and test the wire? If so, would I push the car to check the voltage, as it will not start with the harness unplugged?
Thanks for any advice.

It’s called back-probing.

It’s done without disconnecting the connector.

Tester

Leave the plug connected and back probe the connector to make the connection. If you don’t have some needle point probes you can use a pin and stick it into the back side of the plug where the wire comes out. Then use a jumper wire to connect the meter probe to it or tape the pin to the probe tip.