The easiest route would have been to get a PS32 board with 5V connectors and swap that in. I did that exact repair on a Premier FEF for a friend locally. He got the board set from a tech and I swapped it in for him. Kept the original lighting functionality of the locomotive intact.
Now I've done a few locomotives for myself that had no CV boards. Like John I just run all the lights (usually 6-8 3mm LEDs) off the headlamp circuit.