Yes you can check to see if the LEDs polarity is correct without having to put the cluster back in the car. In my first post I explain how to do it, look for the picture with the jumper wires in it. I did not disconnect the battery, but it would be a good idea to to so working in close proximity to the airbag. I would recommend replacing all of the back light bulbs with LEDs, I do not recommend you change out the indicator bulbs with LEDs. When the system does a bulb check when you initially turn the key, it will think that all the indicator bulbs are blown and the door chime will sound. Yes you can repair the lights on the radio, but it requires a high level of proficiency with a soldering iron. The LEDs are SMDs (Surface Mound Diodes) and are very tiny, and are extremely easy to damage from the irons heat.