Disconnect one spark plug from your car and the engine will still run (not as well but it WILL still work.) If you want a cheap scene look at the escape from the Death Star scene. C-3PO is in a tangled mess of wires, some of them sparking. If you look REAL CLOSE you realize that the sparking wires are simply SPARKLERS!
This may or may not have been a slipup guys. Keep in mind, they were just in a runaway escape pod which crashlanded on Tatooine with a very large THUD. They're both shaken up and have several loose parts. In fact, C-3PO nearly got them both killed when he kicked R2-D2 in his frustration--when he did a washer fell off of R2's dome. It's the same one the stormtroopers found later.