A simple continuity check won't always do it. It is a good general check but sometimes a voltage drop test will reveal more. Basically a meter puts out a very small current when testing resistance. If there is any sort of current path at all, this small current will pass right through and the circuit will appear good. Higher current that occurs when in actual operation might cause the resistance to reveal itself though. That's why a voltage drop test on a loaded circuit is generally more accurate. I'd start with a basic resistance check then do a voltage drop if you still suspect a problem.

Regardless of which method is uses, be sure to wiggle and flex the wires to reveal any high resistance or open circuits.

Also, extensions aren't that expensive to buy or make. If they are suspect, simply replacing them might just be the best idea.<br type="_moz" />