[Shotimes] JBL vs Premium Sound, how to tell decks apart, other problems

[Chris "Zap"]

    I have come across a rather annoying problem while trying to help my 
brother get the stereo working in his '91.  It has what appears to be a 
GenII JBL or Premium deck installed, but no sound what so ever.  His 
speakers have the JBL emblems on them, as well as the amps, so I know it is 
JBL.  I've never had to troubleshoot a JBL system before, so maybe someone 
else on the list has some suggestions.

    Is there a difference between the GenI and GenII decks?  Also, how do 
you tell apart JBL from Premium?  I want to make sure everything is hooked 
up properly and the deck supports JBL.  Also, are there any known issues 
with the JBL amps or wiring in the '91's?  I will end up troubleshooting the 
problem eventually, but if it's something simple I'd like to find out now. 
For that matter can anyone tell me how the fuses work for the JBL in the 
GenI?  I'm guessing there could be a separate fuse for the amps, but I don't 
know.

-Chris