I have a 1986 535i with over 240k miles. I just replaced the water pump and hoses and put in a brand new battery. The car was sitting for two months. The car starts and the dash lights come on but will not turn over. The radio does not come on either. I checked the fuses and they seem to be ok. I couldn't even get the car to start by popping the clutch. The puzzling thing is that when I take the key out of the ignition, the battery light stays on. I had to disconnect the cables to get the light to go off. One thing I did notice is that the battery cables are switched. Not sure if this is a problem because the car ran perfectly prior to that with the switched cables. Any suggestions?

If the battery cables are switched is a BIG problem.ALWAYS make sure the cables are on the proper posts.