Jumper wire
Caution

Voltmeter
is used by connecting the positive (+) probe (red lead wire) to the point where voltage will be measured and the negative (-) probe (black lead wire) to a body ground.

Ohmmeter
Caution

Connectors
Precautions before weldingMazda 6 Service Manual: No.6 windshield fogged
When performing an asterisked (*) troubleshooting inspection, shake the
wiring harness and connectors while doing the inspection to discover whether
poor contact points are the cause of any intermittent malfunctions. If there
is a problem, check to make sure connectors, terminals and wir ...
Mazda 6 Service Manual: Vehicle speedometer sensor (vss) removal/installation
Caution
Water or foreign objects entering the connector can cause a poor
connection or corrosion. Be sure not to drop water or foreign objects on the
connector when disconnecting it.
If foreign materials are stuck to the VSS, disturbance by magnetic
flux can cause sensor output to be ...