Quick and Dirty Amp Bypass? (1 Viewer)

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Rick2000

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West Linn, OR
I got tired of the CD changer not working in my 2000 Land Cruiser and replaced it. I tried keeping the factory amp but the signal output on the new head unit is 4V and the amp is expecting 2V, which makes the new HU really loud. The new head unit has speaker outputs, so the obvious solution seems to be to bypass the factory amp.

Reading up on factory amp bypass, everyone runs a new wiring harness. Why is this necessary? Why can't I just hook my speaker outputs to the factory wiring harness at the head unit where the signal outputs would have been and then bypass the amplifier by connecting the inputs directly to the outputs at the amplifier location, saving myself the trouble of routing a new harness?
 
Good morning,

Welcome to Mud. The stereo also gets its power and ground from the amp. The harness makes it easier and cleaner IMHO. It is not difficult to pull the harness from the head unit to the amp location under the carpet and through the console. I did mine a few months ago.
 
Rick2000 said:
Reading up on factory amp bypass, everyone runs a new wiring harness. Why is this necessary? Why can't I just hook my speaker outputs to the factory wiring harness at the head unit where the signal outputs would have been and then bypass the amplifier by connecting the inputs directly to the outputs at the amplifier location, saving myself the trouble of routing a new harness?
Click to expand...
The problem is the factory harness only has 5 wires for the 4 channel output from the head unit to the amp input. 4 positives and a shared ground. I am sure you noticed the 4 RCA plugs shared the same ground in the aftermarket adapter you currently have. Tying the speaker grounds together would be a surefire way to fry the internal amp in your new head unit ;)

When I bypassed my amp, no aftermarket bypass harness was available. Truly running 8 wires from the head unit to under the passenger seat was easy work, especially if you are lazy and buy bundled wire like I did. I used the Metra adapter for the power and antenna triggers.
https://www.amazon.com/gp/aw/d/B002ODEZ1G/
 
Last edited:
87warrior said:
The problem is the factory harness only has 5 wires for the 4 channel output from the head unit to the amp input. 4 positives and a shared ground. I am sure you noticed the 4 RCA plugs shared the same ground in the aftermarket adapter you currently have. Tying the speaker grounds together would be a surefire way to fry the internal amp in your new head unit ;)

When I bypassed my amp, no aftermarket bypass harness was available. Truly running 8 wires from the head unit to under the passenger seat was easy work, especially if you are lazy and buy bundled wire like I did. I used the Metra adapter for the power and antenna triggers.
https://www.amazon.com/gp/aw/d/B002ODEZ1G/
Click to expand...

Seconding this. In my LX I just ran 4 new speaker wires from the head unit down to the amp and hooked in to the factory harness from there. Took less than 30 minutes to route it behind the glove box and down under the kick panel. Easiest and quickest solution for sure.
 
87warrior said:
The problem is the factory harness only has 5 wires for the 4 channel output from the head unit to the amp input. 4 positives and a shared ground. I am sure you noticed the 4 RCA plugs shared the same ground in the aftermarket adapter you currently have. Tying the speaker grounds together would be a surefire way to fry the internal amp in your new head unit ;)

When I bypassed my amp, no aftermarket bypass harness was available. Truly running 8 wires from the head unit to under the passenger seat was easy work, especially if you are lazy and buy bundled wire like I did. I used the Metra adapter for the power and antenna triggers.
https://www.amazon.com/gp/aw/d/B002ODEZ1G/
Click to expand...

Missed that, actually, but you're absolutely right. That's why I can't use the factory harness. I suppose I could get away with just routing 3 new wires, but routing 3 wires isn't going to be any easier than routing 8.
I also missed that the amplifier has separate outputs for the sub L and R channels that I don't have from the head unit. :frown: Time to figure out what to do about that. HU has sub L/R outputs, no speaker outputs.
 
You will not miss the factory sub(s) if the aftermarket head unit is driving the door speakers. I initially planned to install an aftermarket amp with a real sub as part of my radio install, but decided I didn't need it. The factory door speakers sound so much better being driven by an aftermarket head unit than they ever did being driven by the factory amp.
 
Rick2000 said:
Missed that, actually, but you're absolutely right. That's why I can't use the factory harness. I suppose I could get away with just routing 3 new wires, but routing 3 wires isn't going to be any easier than routing 8.
I also missed that the amplifier has separate outputs for the sub L and R channels that I don't have from the head unit. :frown: Time to figure out what to do about that. HU has sub L/R outputs, no speaker outputs.
Click to expand...
The sub output on head units is just a signal output and not powered. You'll need an amp if you want to run a sub but as others have mentioned the new head unit will make a world of difference in sound, and even cheap speaker upgrades will probably help as these 100 series speakers tend to not hold up well from what i've seen. I'd try the head unit upgrade and maybe new speakers and see if you even want a sub/subs then.
 
OK. So I completed the bypass last Saturday. Here are a few thoughts:

1) Uber thanks to TLCFAQ for a super useful how-to.
2) I just used the Metra harness recommended in the comments above, which fit perfectly and left me a good 4 ft of left over wire. It's not the cheapest option, but it sure made things easier. It also comes with a little connector with 4 wires that I just threw away. I suppose I could have pulled those wires from their connector and used them to make the power connections, below.
3) Sound was noticeably improved even though I didn't replace the door speakers. I don't miss the subwoofers at all. If you're swapping out your head unit, bypass the amplifier.
4) I made the needed power connections under the seat. I couldn't find a plug that fit the S7 connector so I just bought 6 Sumitomo T90 male crimp-on pins and made three jumpers to make the needed power connections. Theoretically, someone could reinstall the amplifier if they wanted to by just pulling out my jumpers and the Metra plug. I don't know why that was important to me.
5) I was going to use connectors to connect the speaker wires from the head unit to the speaker wires in the Metra harness but the difference in wire gauge was just too much. The wires from the head unit were tiny. Nothing that would have crimped to one side of the connection would have crimped to the other side. So I ended up soldering the wires together.
6) Also added a Y-connector to connect up both antennas. This really improves radio reception. When the head unit was first replaced I lost a significant amount of radio reception. Now that I'm using both antennas my reception is at least as good as it was with the original radio. In fact, I now leave the mast antenna pretty much all the way down and get better reception off just the window antenna than I was getting when I only had the mast antenna connected. That window antenna is pretty good. If you insist on only picking one antenna or the other, pick the window antenna.
 
Quick question for the 98-99 guys. Does the Metra harness work for 98 and 99? Everywhere online says 2000-2009.

If the metra bypass harness does not work for 99, is my easiest option to run wire from the head unit down to each speaker...or is it easier to run new wires from the head unit down to the amp harness?
 
It would be one million times easier and cleaner going to the amplifier location/harness, rather than each speaker.

And just another quick note about the original thread question... sending amplified signal (speaker level) to another amplifier will almost never produce reasonably good sound. Using clean, low-level RCA signal would be ideal.
 
I had originally wired the signal outputs to the amplifier, but amp was expecting a 2V signal and the head unit output a 4V signal. This meant I couldn’t use a volume greater than 3 without fear of permanent hearing loss.
 
ogsuv said:
It would be one million times easier and cleaner going to the amplifier location/harness, rather than each speaker.
Click to expand...
I completely agree. Running the wire is even easier if you use a bundled wire, similar to what I linked a few posts ahead.
 
Yeah I clicked on your link a couple days ago but Amazon said nothing found.
 
@Tanner H did this work for your Cruiser? I have a '99 LX with the Nakamichi headunit. Replaced it for an Alpine double din. Any idea if this works for the Nakamichi?
 
Nevermind. I should've done a little more research before asking that question. Based on the tlcfaq (thanks for posting that), my nakamichi harness is different than the land cruiser. Unless I'm missing something it looks like this harness won't work for me.

I called metra to verify and they told me they have nothing for the LX. Looks like I'll have to cut and splice the speaker wires to bypass the amp.
 
ah damn. yeah sorry the naka system is a different beast. I have a standard 99 land cruiser.
 
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