Car Stereos: Hooking up stock amp/sub, to an aftermarket head unit, lexus ls400, rockford fosgates

Question
QUESTION: I have a 1990 Lexus LS400, and I replaced the stock head unit with a Pioneer DEH-5100UB. My friend installed it, but said I CAN NOT use the stock amplifier or subwoofer. Well my sound quality is not good. I have Rockford Fosgates in front and MTX in back. Both sets of speakers are just average($79 a pair), and it is lacking that "deep,whole sound". How can I hook up the amp and sub ? Any input will help, thanks Brian................ HHHEEELLLPPP !!!!

ANSWER: Hi Tom,

I don't think I've ever tried to integrate the rear-deck subwoofer in this vehicle, but from what I can tell it should be possible.  There's a separate 6-pin plug in the factory radio harness; this supplies the signal to the subwoofer amp.  The signal wires in the plug are pink and blue.  I'd try wiring these to an RCA plug.  The easiest way is to buy a set of speaker wire with RCA ends; you can find this at Radio Shack or most electronics stores.  Cut off the RCA end, with a suitable length of wire.  Splice the positive wire from the RCA plug to the pink wire in the factory 6-pin plug, and splice the negative wire to the blue wire.   Then connect the RCA plug to a subwoofer output jack on your head unit.  

You'll also need to make sure that the factory remote wire is connected to the blue/white output from the Pioneer head unit.  The remote wire should be pink with a blue stripe, located in the large 10-pin factory radio plug.

Hopefully, this should get the stock subwoofer working, and you should be able to adjust the volume using the subwoofer level control built into your head unit.

Hope this helps!

Brian

---------- FOLLOW-UP ----------

QUESTION: Brian, that info helped and I thank you !! Wondering about the amp though, can I hook that up also ? I'll let you know when I've tried hooking up the sub. Thanks again !!

Answer
Tom,

According to the information I have, the only factory amplifier in your vehicle is the subwoofer amp.  The directions I gave before--if they work--should turn on this amplifier, and it will run the sub.  The other speakers in the vehicle were originally driven by the stock head unit, not by another amplifier.

Hope this helps!

Brian