I forgot does the L300 have a level control? Did you try bypassing that? .
RE : JBL 4333/ L300
just replaced diaphragm in 077 ,works normal [no I did not test with a 9 volt battery-never have] *,multimeter- Also Connected tweeter to another system. The tweeter IS working normal < the l pad is Working Normal. no signal from my cabinet. Being just a music lover and nothing else ,my conclusion is the Problem lies in the crossover