Check the wiring harness and look for weak spots. You can also test the resistance between the wire ends with a multimeter, it's easier with digital though. You can pick up a cheap digital multimeter for around $30 and they are well worth the cost. Also make sure to check your ground wires, a bad ground can cause a lot problems. Another thing you could try if you're grounds are good is jump a wire from the battery to the starter to see how it turns over. If it turns over right away then it's something in your harness. But if it doesn't then I would suspect something with the starter being a problem. I'm not extremely knowledgeable with the 660 wiring but electrical is always the same pain in the rear to diagnose problems.