I cannot help you with the converter location, but when you find it, check the 115 VAC power going in. If it is there, disconnect the output wiring from one side, and if you do not have the old ferroresonant buzzing sound, then your converter is bad. The best solution is to replace the old boat anchor with a new 3-stage converter, like a WFCO or Parralax. There are lots of threads about these. If you are electronically talented, you can fix the old one usually by replacing the internal capacitors, for about $12. It all depends on your talents and budget.
T.V.:'05 Dodge Ram 2500 4x4 Quad Cab Cummins