2001 lexus gs430 mark levingston

You must have tapped the wrong wires after the amp.  If the speaker changes volume the converter will change volume.  You really need to verify that you have the actual speaker wires coming off of the amp.

Lexus 2001 GS 430 4DR Sedan

WITH MARK LEVINSONW/O MARK LEVINSON
WITH MARK LEVINSON 
 
W/O MARK LEVINSON RADIO HARNESS  
Wire Function Color Note Fuse # Size Location
+12V DC Battery(Constant) Blue / YELLOW    Dome  10 Amp  Junction block on passenger side 
Switched Accessory Gray  To CD changer also  Radio 2  15 Amp  Junction block on driver side 
Ground  WHITE/ black   
Power Antenna  WHITE/ red  BLACK/ white for antenna A; WHITE/ blue for antenna B. 
Mute  YELLOW /GREEN (amplifier)  Telephone and CD player mutes are blue/orange, and navigation ECU mute is GREEN/ red, all from the amplifier. 
Left Front +  Black  Line level output 
Left Front -  Red  Line level output 
Right Front +  White  Line level output 
Right Front -  Green  Line level output 

AMPLIFIER OUTPUTS  
Wire Function Color Note Fuse # Size Location
12V DC Battery Blue / YELLOW    Radio 1  30 Amp  Relay box 1 in engine room 
Remote Turn On (input)  Pink/blue  Accessory wire 
Left Front Mid +  Pink  Or blue/black going to navigation unit pin 1 & out at pin 2 as pink (if equipped). 
Left Front Mid -  Violet  Or blue/red going to navigation unit pin 10 & out at pin 11 as violet (if equipped). 
Right Front Mid +  Light green   
Right Front Mid -  Blue   
Left Rear Mid +  Black  Passes thru the telephone transceiver and speaker relay. 
Left Rear Mid -  Yellow   
Right Rear Mid +  Red   
Right Rear Mid -  White   
Subwoofer 1 +  Lt.GREEN/ black  Or blue/black 
Subwoofer 1 -  Lt.GREEN/ red  Or blue/red 

AT SPEAKERS  
Wire Function Color Note
Subwoofer 1 +  Brown   
Subwoofer 1 -  Lt.GREEN / WHITE   

RADIO HARNESS  
Wire Function Color Note Fuse # Size Location
+12V DC Battery(Constant) Blue / YELLOW    Dome  10 Amp  Junction block on passenger side 
Switched Accessory Gray  To CD changer also  Radio 2  15 Amp  Junction block on driver side 
Ground  WHITE/ black   
Power Antenna  WHITE/ red  BLACK/ white for antenna A; WHITE/ blue for antenna B. 
Mute  YELLOW /GREEN or blue/black (amp)  Telephone and CD player mutes are blue/orange, and navigation ECU mute is GREEN/ red, all from the amplifier. 
Left Front +  Black  Line level output 
Left Front -  White  Line level output 
Right Front +  Red  Line level output 
Right Front -  Green  Line level output 

AMPLIFIER OUTPUTS  
Wire Function Color Note Fuse # Size Location
12V DC Battery Blue / YELLOW    Radio 1  30 Amp  Relay box 1 in engine room 
Remote Turn On (input)  Pink/blue  Accessory wire 
Left Front Mid +  Pink  Or blue/black going to navigation unit pin 1 & out at pin 2 as pink (if equipped). 
Left Front Mid -  Violet  Or blue/red going to navigation unit pin 10 & out at pin 11 as violet (if equipped). 
Left Front Tweeter +  Brown   
Left Front Tweeter -  GREEN / WHITE   
Right Front Mid +  Light green   
Right Front Mid -  Blue   
Right Front Tweeter +  Blue/black   
Right Front Tweeter -  Blue/red   
Left Rear Mid +  Black  Passes thru the telephone transceiver and speaker relay. 
Left Rear Mid -  Yellow   
Right Rear Mid +  Red   
Right Rear Mid -  White   
Center Channel +  Brown   
Center Channel -  GREEN / WHITE   
Subwoofer 1 +  Brown   
Subwoofer 1 -  GREEN / WHITE   

AT SPEAKERS  
Wire Function Color Note
Left Front Tweeter +  Blue   
Left Front Tweeter -  Light green   
Right Front Tweeter +  Red   
Right Front Tweeter -  White   

I spliced into the input signal wire from the hu to a loc to amps the signals work and i hear the music fine but i lost the control of the volume i have no control of it whatsoever.

Those wires you taped into are already line level, no need for a Line out converter.  Just cut a RCA wire and slpice into those wires again.  Maybe thats what went wrong. LOC bring speaker level down to line level, you are already at line level just need to convert wires to rca jack and plug into amp.

good luck, Frank