I was asked to install a new High Pressure Sodium fixture near an existing one. From the existing fixture I conduited 50 feet and set the new fixture. Both of these fixtures are controlled by a photo cell on the roof. The existing fixture was existing and old. It must have had a bad starter because it would go on and off at regular intervals. When I first installed the new fixture and tested it, the old and new fixture would "take turns" being on. I wasn't sure what was going on with that. I do know neither had their own photo cell.
Now two months later, the old fixture only blinks and the new one doesn't work. I tested the voltage at the new fixture (feed 120V) and at the socket (54V), so I think the transformer is shot.

Here is my question. I can see why the old fixture is not working (old), but could a problem with that fixture ruin the new fixture?

Let me know if I left out any important details.

Many thanks,