JBL Synthesis Amp Bypass / Metra 70-8117 Install

[heavymetalbebop]

So after much tinkering with an aftermarket HU install and not much satisfaction with the sound quality running it through the JBL amp, I purchased the bypass harness to see how the HU's built-in amp sounds. Unfortunately, and pardon my ignorance, but this harness came with zero instruction on how it is implemented into the system.

So I'm trying to avoid a huge project if it's not necessary (i.e. Ripping out all the passenger side panels to run the wires). Does the harness hook up at the amp in the trunk and wires run to the HU behind the dash? Or does the harness hook in behind the HU and wires are run and connected to the aftermarket amp?

 

[adamderry]

Ive done this to my 4runner, yes you must run the harness from the oem amp harness socket in the rear to the headunit in the front. Its really not that bad to install but keep in mind that you will lose the sound from your sub if you go this route

 

[heavymetalbebop]

Okay I ran the wires today and it was easy, but I've lost the sound in the trunk speakers and front center channel. Is this a result of the amp bypass or did I miss a connection here?

 

[heavymetalbebop]

Bump

 

[adamderry]

This is because you no longer have power to the amp. Your headunit is the only power source now and it only has 4 channels which power the door speakers

 

[jward6004]

Future aftermarket h/u install with factory JBL speakers

I recently bought an 2004 4Runner Limited and it has a subwoofer and connected amp installed in it. Unforunately the sub is in a external sub box that is hogging up cargo space. So my solution is making my own fiberglass sub box to fit in the place of the factory JBL blown subwoofer flush with the side panel in the trunk.

I'm commenting on this thread because I'm trying to figure out what to do with the factory amp that connects to the door speakers and stock stereo... I'm planning on replacing the stereo later and want to avoid creating more work for me down the road. Does anyone have any suggestions on if I should mount the factory amp so it runs my JBL door speakers or would you suggest that I invest in the bypass harness and run that to the back of the stereo for when I replace it with an aftermarket headunit??

Based on the amp power comment below, the factory amp should be able to run my door speakers and the sub amp would run power to my aftermarket sub, correct?

 

[Dlaird15]

Okay I ran the wires today and it was easy, but I've lost the sound in the trunk speakers and front center channel. Is this a result of the amp bypass or did I miss a connection here?

given the lost subs and center speakers, are you satisfied with the project? I'm trying to get my HU installed and am thinking the amp bypass is easier and more reliable than using the amp interface harness from metra or PAC.
Eventually I will upgrade the old amp/sub and re-wire whole system with RCA but for now I just want the new HU installed!