My Hayward SP-581 12 volt fixture stopped working last year. Finally got around to changing the bulb when opening this year. Took out the unit which is submerged. Changed out the bulb and it is still not working. Unit looked fully sealed and dry inside. I'm not too familiar with transformers and how these units connect. I tested at the switch and it was operating and exporting 120 volts to the transformer. Can you point me to where or what I should test next? Thanks in advance for any help which is greatly appreciated.