Hi, if you spray your high tension wires with wd-40. Before getting in to start the car on a wet morning for example. If car is okay then it is the wires. Also you could take a spray bottle of water and spray the wires only when they are good and dry. If car acts up you have it again. If not try the distributor exterior next.. The wd-40 repels water for a few days to give you a temporary cure as well. That aids in positive diagnosis. Just nice to be certain before you spend money. Also as someone mentioned you might visulise the sparks leaving the wires at night. But the other two methods are prefered by me.