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040 hardtop turbo
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320 Posts
Are you sending speaker-level output to the amp? The amp expects line-level signals.
You have the same head unit so I would imagine so.

Also, I don't know if you guys noticed, my Metra 70-8112 harness uses pin 12 as the ground shield for the 4 line-out RCA pins, but that is incorrect. Pin 12 on the factory harness is the "fade" signal to the stock amplifier, so I removed pin 12 on the Metra harness and connected that wire to the black ground wire on pin 11.
I'm exhausted..I officially regret ever finding this stupid thread. It's been more of a punishment lol. I very cleanly re-pinned the ground to Pin#11 instead of #12 on the Metra 70-8112 for the RCA's. Result was 10 times worse.

Pin 12 is another ground, signal ground. Maybe you have a wierd integration harness. I suppose you can try 12 instead of Pin 11. It will or will not work. Pin 11 is the "common" speaker ground.

After more detective work, in Stu’s little ms paint image he has the RCA ground going to #12 even though Ishii’s schematic shows #11. So Metra’s default configuration was correct, which makes sense. Note that Stu himself may be oblivious of this because he asserts somewhere early in the thread that it should go to #11 lol.

Pic:
https://www.dropbox.com/s/xuqzn08jn5h66jo/2018-12-04 10.06.53.jpg?dl=0


Question.. why in his images, does Stu appear to have the ground wire (#11) from his metra 15-pin adapter (which goes to R6) spliced into the ground from his HU going to the chassis? (Ishii says just ground the HU straight, so does his schematic) Its the pics that show this but he contradicts himself buy saying that ground wire is tied to his RCA's but also in his ms paint pic he says to wire it to the HU directly... too much inconsistency ughh!!


Here's a link to my harness..
https://www.dropbox.com/s/pn24cfim1lpa27d/2018-12-03 20.44.36.jpg?dl=0
note: I ran a new pin for #2 dimmer and omitted #8 the solid blue power antenna wire

Thanks!!!
 

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040 hardtop turbo
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320 Posts
In addition to my previous post... I’m planning on ONLY using my rear glass antenna as opposed to the powered (fishing pole) antenna (I will use Metra 40-GM10 adapter harness to make the small plug a larger one) since I dont want to deal with wear and tear on the motor and in the future will probably shave it anyways.

So just to be clear, the ONLY reason to have the female 6 pin and 10 pin connector is for the power "fishing pole" antenna? because I did not install that connector (unintentionally) and as it seems everything works fine, except for the antenna raising. But, I did plug in the power antenna cable into the back of the new HU, so was that pointless to plug it in?
So.. that means I can completely delete the Metra 71-1761 (male IH1/IH2 connectors.. I noticed some of y’all call them female pins lol) right?
 

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Master Shit Fixer
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3,180 Posts
Are you sending speaker-level output to the amp? The amp expects line-level signals.
You have the same head unit so I would imagine so.
This is an issue. If you are sending speaker-level outputs to the stock amp, your are overdriving it. The amp expects line-level signals (RCA connections). In my case, the stock amp is gone and I am sending the RCA outputs of the stereo directly to the line-level inputs of an aftermarket amp. I am not using any of the speaker-level wires on the Metra harness.

Can you post a picture of the radio harness and Metra harness, showing which wires you have connected to each other?
 

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040 hardtop turbo
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320 Posts
This is an issue. If you are sending speaker-level outputs to the stock amp, your are overdriving it. The amp expects line-level signals (RCA connections). In my case, the stock amp is gone and I am sending the RCA outputs of the stereo directly to the line-level inputs of an aftermarket amp. I am not using any of the speaker-level wires on the Metra harness.

Can you post a picture of the radio harness and Metra harness, showing which wires you have connected to each other?
Okay, here's a video of me verifying the harness against the schematics. You can stream it rather than downloading, I love dropbox.
https://www.dropbox.com/s/b7a7vsyd2hco3rr/2018-12-05 09.02.10.mov?dl=0

Here's closeup pics of the connectors and connections.
https://www.dropbox.com/s/reifouujx4wevlt/2018-12-05 09.17.08.jpg?dl=0
https://www.dropbox.com/s/avt1l5jlci3n6lg/2018-12-05 09.17.27.jpg?dl=0
https://www.dropbox.com/s/mfxzt27us0koeed/2018-12-05 09.18.16.jpg?dl=0
https://www.dropbox.com/s/xe7jbt7ofp00uek/2018-12-05 09.18.42.jpg?dl=0

SOS! :)
 

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Master Shit Fixer
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3,180 Posts

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040 hardtop turbo
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320 Posts
You have the speaker outputs of the head unit connected to something (can't tell from your pictures). But they should NOT be used. You need to run RCA patch cables from the back of the head unit (not the wiring harness) to the amp's signal-level inputs somehow.
You can watch the video if you want.

Just to share, I think there was something wrong with my amp. Or perhaps a compatibility issue. I ended up bypassing the stock amp and everything works perfect.

I was lucky enough to get help from Stu, he was beyond knowledgeable and very gracious with his time. Even though I couldn’t get this working, it was worth it just to have to opportunity to chat with him.

For the record the stock amp is 40w so for those of y’all who have upgraded the front and rear speakers (should be everyone lol) and want to have a setup that’s balanced/proportionate you can very easily install a nice modern mono or 2ch amp without any permanent modifications to your Supra and power a 10000 times better subwoofer :D
 

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7 Posts
If the stock amp is only outputting 40w, how was it driving the speakers and sub?

My car doesn't have a sub. Does that mean the wiring wasn't ran for it either? I don't have a IH3 connector. If I wanted to add a sub using the stock amp, that's pretty much out of the question right?
 

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Master Shit Fixer
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3,180 Posts
If the stock amp is only outputting 40w, how was it driving the speakers and sub?
Poorly, relatively speaking. 40W is not nothing (lots of aftermarket head units have 45W internal amps). But even a few watts will produce sound from a speaker.

My car doesn't have a sub... If I wanted to add a sub using the stock amp, that's pretty much out of the question right?
Yes, out of the question. Add an amp for the sub, or ditch the stock amp and get one that will drive all of your speakers.
 

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hello, my car already had a bypass with a Metra wiring harness. How do I supply power to the amp so that I can still use the factory sub? IH3 is still connected.
 
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