I bought a lot "5 cars" from e-bay. Three of them are Atlas Illuminated passinger cars, and 2 are another brand. But I'm not sure if them 2 are Illuminated. The probem is only one of them lights up and that is only now and then and it seems to be in certain parts of the track. Like on a corner or maybe a rerailer just every now and then. Do I just need to clean the contact area or is the something I need to take a part to diognose a problem.