https://www.youtube.com/watch?v=pDzRsOpne_Q

Video tutorial on how to test an electrical circuit for continuity/break in the wiring or a poor connection.

Procedure:
-a multimeter is required for this test
-using a multimeter, set the multimeter to the lowest ohms increment or to the continuity setting if equipped
-put the test probes together to determine the lowest value the multimeter will show a reading of (if the reading is not 0, this can be caused from a low battery or dirty test probes)
-determining where the wire run, check the continuity/resistance between point A to B by placing the testing probes on the wire contacts
-determine the value given
-if there is an excessive amount of resistance or no continuity within that particular wire you are testing, there could possible be a break in the wire or a loss connection
-inspect the wiring for any corrosion in the contacts
-inspect the wiring for any breaks in the casing
-inspect the wiring for any corrosion leaking out of the casing
-pull along the wire to see if it "stretches" (broken wire within the casing, which is still held together by the exterior casing/insulation)
-using a needle, penetrate the casing and test for continuity/resistance in the plugs or between points A and B
-once the problem is found, take the correct actions to resolve the issue

Causes:
-corroded wiring
-corroded connectors
-break in the wire
-break in the casing which caused the wire to corrode
-break in the casing to cause the circuit to short out
-constant bending or strain on the wire which caused the wire to crack

Possible Repairs:
-if contacts are corroded, clean contacts using a solution or an abrasive pad
-if casing is broken, repair using silicon, shrink tube, or electrical tape
-if wire is broken, a section can be cut out and replaced by soldering or using solderless crimp connectors to attach the new wire
-the entire harness can also be replaced if chosen