Ok. I cannot find a coherent all in one thread that fully outlines how to 100% bypass the amp, so with the disclaimer that I've never *actually* done this and don't know a lot of variables such as impedance of the OEM speakers nor impedance at the output of the Scion stereo I'm going to attempt to do that for you here. I am going to assume that you're trying to install a Scion stereo, as that's what we are discussing in this thread. Doing this for an aftermarket stereo would be eerily similar. All pin numbers are taken from the 2004 LC Electrical wiring Diagram, it's all I have available. If you want pin outs verified I would gladly do that if you can source me the correct year/model EWD.
You will need to use a 2nd harness to connect to the Scion stereo. The cheapest/easiest to source would be
Scosche Reverse Harness This will plug into the Scion head unit to get the power in and the signal out of it. If you have the 20 pin connectors you will need to pull 4 short runs of wire, because that connector uses a common ground for the signal from the stereo to the amp and the Scion unit uses a closed loop to each speaker.
You would then have two options. You either remove the pins from the OEM plug and insert them into the correct location in the Scosche plug, or you would cut the OEM harness and solder/heat shrink (or your preferred method of connecting) to the Scosche harness. I have not verified that the OEM plugs from a LX/LC will fit into the Scosche harness.
Here are the connections for the 20 pin LC harness:
- R36 pin 1 to Scosche yellow
- R36 pin 2 to Scosche orange
- R36 pin 8 to Scosche gray
- R36 pin 9 to Scosche white
- R36 pin 11 to Scosche red
- R36 pin 13 to Scosche blue
- R36 pin 18 to Scosche purple
- R36 pin 19 to Scosche green
- R36 pin 20 to Scosche black
The pin out for the LX 20 pin connector isn't exactly complete over on the
"Stereo Upgrade" page so you would need to verify via LX FSM before making connections.
Now, back to that tricky common ground that we discussed earlier. Your 20 pin harness wiring won't have anything to hook to the FL-, FR-, RL- or RR- on that Scosche harness. You will have to pull 4 wires from the stereo area to the OEM amplifier area while keeping track of which one has been hooked to which corner's - output.
Good news is that if you have the Nakamichi system then you won't need to pull any additional wires.
Here are the connections for the 22 pin LX Nakamichi harness:
- Pin 1 to Scosche yellow
- Pin 5 to Scosche blue
- Pin 6 to Scosche white
- Pin 8 to Scosche purple
- Pin 9 to Scosche green
- Pin 10 to Scosche red
- Pin 11 to Scosche black
- Pin 13 to Scosche orange
- Pin 17 to Scosche gray with black
- Pin 18 to Scosche gray
- Pin 19 to Scosche white with black
- Pin 21 to Scosche purple with black
- Pin 22 to Scosche green with black
Now that that's all connected up, we have a means to plug the stereo in and can move on to the connections at the OEM amp. These pin numbers are assuming that the LX amp pin outs are the same as the LC amp pin outs posted on tlcfaq. I have no means to verify this information but haven't found anything stating the amp connectors are pinned in any different order. Due to the different outputs on the Nakamichi system I cannot believe the amp pin outs are the same for it; however, I have no means to verify this as I don't have the LX wiring diagram. Here you would, as mentioned on tlcfaq connect:
- S7 pin 3 to S6 pin 7.
- S7 pin 2 to S7 pin 9.
- S7 pin 10 to S6 pin 13.
That will get the power/ground into your head unit.
Moving on to the signal wires we would connect
- S7 pin 5 to S6 pin 2
- FL- wire that was added to S6 pin 9
- S7 pin 6 to S6 pin 1
- FR- wire that was added to S6 pin 8
- S7 pin 13 to S6 pin 4
- RL- wire that was added to S6 pin 11
- S7 pin 14 to S6 pin 3
- RR- wire that was added to S6 pin 10
Now after all of this pin swapping and wire pulling we have successfully created a path from the battery/ignition switch to the new head unit to power it on. We've also created a path from the head unit to the speakers in the doors while fully bypassing the OEM amp under your seat. There are no Subwoofer outputs on the Scion head unit so it would have to go unused.
A few notes:
- If this doesn't make sense to you, please don't attempt it. There's no reason hacking your wires just for the sake of hacking your wires.
- While they are OEM and look quite nice, those Scion head units are under powered compared to aftermarket units. Most are 10-18RMS per channel.
- The OEM speakers aren't the best
- If using an aftermarket head unit, it's really not much more difficult to pull new wire to all 4 doors directly from the head unit.
- If I've mis-typed or gotten anything wrong please let me know and I'll edit the post.
- I don't see the true benefit of going through all of this hassle for not much of an upgrade, in my opinion.
