Whether it is quickly checking an injector harness, sensor or solenoid valve of some kind, you may need to check whether the delivery harness is either supplying power or a signal. A very quick way to determine this is by using a test light or sometime referred to as a noid test light.
However you can easily make you own with a 12v light, a small amount of wiring, safety pins and some crocodile clips.
An easy fix to perform a simple test without the need to necessarily buy purpose test lights for your vehicle…