Even most advanced DIY's and troubleshooters are not familiar with Voltage Drop Testing. This video shows a real life example of how lack of knowledge of this important skill can lead to misdiagnosis!
Further, voltage drop is illustrated in an easy to follow manner so you will understand voltage drop for the rest of your life without having to look up how to do the testing or when it might apply.

Other videos with voltage drop test or relevant material:
Fuel pump testing:    • Low Fuel Pressure,Lean Condition diag...  
Diagnosis and testing of relays:    • Relays- Understanding, Diagnosis and ...  

Also for many electrical testing tutorials and videos see my friend Terry's channel Stuzman52    / stuzman52