[BILL]

You've check your filters? One lead is for the lamp on the dial , , 7m ,sounds like the spark plate GM radio use a thin piece of paper ,it's there to filter 6volt line , if it's not shorted it shouldn't give you any problems,
I once bought out an old radio shop that did auto radio work ,in with all parts equipment,and radios was a 8 tube 55 Ford radio with "JUNK" written on it ,I worked on it since I've usually won't let an auto radio beat me, what I found was that it had had a shorten buffer and as usual some one kept trying to keep playing by replacing the vibrator ,what happen vibrator hash burned up,there was burn marks even on the chassie! The shop I bought out had tried to repair the radio only using the wrong vibrator hash, the radio had a BAD buzzing sound ,really bad, the shop didn't know what to do ,must have told the customer radio was unrepairable .I found the right vibrator hash repaired it , today that radio is in a 55 Ford in Porto Rico