First, the obvious, stupid stuff... (been there, done that):

a) Are there any internal fuses? Often, there will be board-mounted fuses and/or fusible links to protect sub-assemblies not immediately visible. If you have a schematic (you DO have a schematic??), look for one of these symbos:

https://qph.fs.quoracdn.net/main-qim...40b083cc4e4f-c

b) Corroded and/or broken trace in the voltage path. Follow the voltage for the lamps back to the source and look for anything that could cause a discontinuity.

c) Are you sure you are using/measuring to the correct 'ground' for those lamps? In some few cases, the lamps are part of the active circuit, such that voltage must be measured across the correct points, not to the common ground.

Again, I have no schematic, I am just enumerating the stupid-before-doing-surgery-diagnostics-as-general-practice. Please let us know.

Peter Wieck
Melrose Park, PA