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Bypass factory AMP 92 LS400

I am looking at bypassing my factory amp in my 92 lexus LS400, but I cannot find any pin diagrams to tell me which pins my speakers are connected to. Does anyone know where I can find one or the easiest way to find out which two wires go together?

Also, if I bypass the amp then what will this affect? will my sound just be quieter or will some speakers not work? like the factory installed subwoofer?

Also, if I am to understand this correctly, bypassing an amp is just taking the positive and ground from a speaker where they are connected to the amp and connecting them outside of the amp, correct?

Also, something confusing is the location of the amp. I have checked under the CD changer in the back, and there is nothing there. Right above it is an aluminum box but a part number search indicates this is a suspension computer for the auto-leveling, but on the left side of the trunk by the antenna there is a black box under the paneling, is that the amp?

Sorry for all the questions, just want to make sure I get it right!

You have to have an amp, are you replacing it?

I don’t see how that can be done and still have the entertainment system.

The amp is what produces the sound.

In the past, the stereo system had the amp in the unit. So if you swapped out the stereo the amp came with it.

But today’s vehicles have a head unit, which is the component in the dash. And the amp is a separate unit from the head unit.

So without an amp, no sound.


The amps were in a few locations, did you look under the passenger seat? What sound system do you have? I can get the diagram tomorrow at work but most likely won’t have a chance to post it up until the evening. A good stereo shop will be able to help you out. The amps were know to fail in the LS even when they were new.

If you want to bypass the factory amps, it is best to buy a replacement stereo with an appropriate rated output for your taste and re-wire to the speakers. Just by-pass the entire factory system. You’ll be happier.

When they are factory installed componenet systems , you can not usually delete one unit drom the chain.
I’ll bet you find the ‘‘radio’’ or control head has zero amplifying capability ( it’s merely a pre-amp )…you will get no sound.

WHY do you want to do this ?

I purposely spend good money to get the good sound systems in mine.
A value my wife cringes at but concedes when she hears the difference, at LOW volume, between the JBL or Bose systems and the plain jane. ( like watching color tv or black and white )

So I want to get rid of my factory system, my cassette deck and CD player don’t work so I’m trying to buy a new stereo. Personally, I don’t care about volume, I literally just want to plug in my phone since my local stations are terrible. I looked at the FM modulators and they have such mixed reviews I figured I may as well go all out and get some neat features with a new radio.

I have not checked under the seat, but I’m pretty sure it’s on the left side of my trunk.

Either way, I believe I found a solution through

They have the stereo and a bypass kit, plus vehicle specific instructions. So I may have my solution. Thank you for your help though!

Now that I understand what you want, I was going to suggest crutchfield. Their phone help is great, too. Good choice!

Just be careful the new head unit you get will probably be rated for 4-8 Ohms speaker impedance and the Toyota JBL systems mostly use 2 Ohm speakers. This could cause problems for the output amp. in the receiver.