You have either a ground issue, or a battery issue. Doubt the issue is with the resistors since you have problems with the radio and the headlights.
Tighten the battery terminal connections to start then go from there.
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2000 Boxster Tiptronic
2003 Boxster
2003 996 C2 Cab
2002 996 (SOLD)
1986 944 (gone but missed)
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