PAC is dedicated to the preservation or authentic restoration and use of Packards; if you must consider non-stock modifications, here's the place.
One question is which flasher you used to replace the burned out item. The original TungSol is full thermal with two sets of contact points - one for the turnsignal bulbs and one for the indicator light. The modern 6v replacement which is typically a 535 has contacts for the signal bulbs but a transistor to operate the indicator light. There have been several reports on other forums the modern replacement works for the signal bulbs but does not work the indicator light. Not sure if the modern flasher with a transistor can work with the positive ground since transistors are polarity specific but something to think about. Also on the modern item if the wiring was reversed and the transistor saw the full load of the bulbs or the input voltage then it could have been destroyed.