ORIGINAL: CGRetired
A continuity check will do but the voltage drop across the internal resistance of a wire is very small. What you detect, if you had a problem, might be caused by corrosion at the connections between the extension and anything it is connected to. At any rate, the resistance is very small and hard to detect.
I was going to reply in the same way... However ChuckW's idea of using a meter while performing a WiGGLE test is not a bad idea to help spot breaks or potential problems that may arise due to vibrations.
However voltage drop is not very telling otherwise, on our fairly short cable runs....
I own a Time Domain Reflectometer which I've used on RC cables, and even this fairly sensitive instrument has a hard time with them.