What are these things in my LED light string?
A typical string of LED holiday lights uses either resistors or capacitors to limit the current, as well as a reverse-blocking diode, as shown in the below schematic.

Capacitors tend to be less common for some reason. Perhaps it's cost-related, but I wouldn't expect a capacitor to cost a whole lot more. Anyway, if you can isolate one of the canisters and measure resistance across it (assuming your meter has a compliance voltage high enough to cause the diode to conduct, usually between 0.6 and 1 volt), you should get a rough idea of the total current-limiting resistance, though this does not take into account the resistance of the conducting diode.