I have a 2005 S type with the Premium alpine system and I installed an aftermarket radio and had the wiring harness wired right but once hooked up no sound came from the speakers. I called a friend and he said I needed a dual amplifier bypass. Is this needed? Any suggestion can help.

 

Check to make sure your speakers are wired to your new head unit. Trace the cables. Did you originally have the premium amplified system or standard non amplified?

 

You'll have to provide detailed info on how this was wired. Check to see if the aftermarket head unit is daisy chaining the aux power feed to the external amps (Usually the blue wire off the aftermarket head unit's proprietary harness). Then, ensure that the low-level RCA jacks on the head unit are wired to the external amp's input. These cannot take the speaker outputs from the aftermarket head unit. Some external amps go into "protect mode" when the input is overdriven, and therefore immediately shut down. I know that I have to design my own harnesses to do this with the Premium system in an '02, so I believe you're running into the same challenges. There are many threads here by members who've run into the same challenges - but overcame them. Do a search. Plenty of lessons learned.

 

I think I would unwire it and put the old one back in.

 

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The factory "Alpine" amplifier that runs the speakers will not give any output without the factory head unit, since the audio signals are digital on the D2B network.

If you want to put in an aftermarket head unit then you cannot use the factory wiring for the Premium Sound, at all.

The post 2002 S-Types were factory wired for both Standard and Premium sound, you will find the cables/plugs for the door speakers already there in the door cavities. At least you should find them, cars delivered with Standard sound had the Premium wiring in place, should be the other way round too.

You really need to study the cars wiring diagrams.