I was pulling my hair out trying to replace the factory head unit in my 2003 Toyota 4Runner that came with the factory JBL audio system (amp and sub in trunk). I was minutes away from just driving my truck off a cliff out of frustration with how many different poorly documented factory wiring options there were for one freaking make/model of car. This was my 4th wiring harness I purchased and the only one that worked. It works perfect. Please note however the product does not match the picture in the description. There are no RCA cables at all, and the black box is a different shape see the attached picture. However, it seems to work fine by hooking up the eight wire leads instead of four RCA's.I will explain what was wrong with the other three harnesses, as I figure people with the same vehicle as me may be running into the same issues and this is the answer.1st attempt - Metra 70-1761 - This is the standard Toyota 87+ wire harness, however if you have a JBL factory headunit these wires will not fit. This is for non JBL headunits, that only have 4 door speakers. I had to remove 6 panels and take my dash half apart to get to see these factory wires.2nd attempt - Metra 70-8113 - Fit one of the three factory JBL harnesses, and the new head unit powered on, however no sound. Found out part of my factory JBL system was an amp in the trunk that powers 10 speakers. This harness didn't provide the necessary data signal to the amp to turn it on, so there was no sound. The blue "amp on" wire did not work.3rd attempt - Metra 70-8117 Amp Bypass Harness - Decided the bypass the amp and center/tweeters all together and just hook up the 4 door speakers with this bypass harness. It did not fit the factory harnesses, and with some extensive googling for wiring guides i found out the specific model factory headunit i had (JBL 56827) has three plugs on it, however none of these 40 some wires work for bypassing. They are all for audio-in expansions and steering control and other stuff. This is about where I lost it.4th attempt - This - It doesn't look at all like the picture. There are no RCA connections as pictured, and the black box is completely different. My new headunit had RCA connections which made me think this was not going to work. I figured it was worth a shot though so I wired it up to the 8 F/R L/R speaker leads. IT WORKED! It was sounding a bit distorted so I tweaked the attenuator knob and now it sounds incredible and clear. There is about a 5 sec delay from turning my truck on and off till you hear any sound, however it seems to work consistently. There is no steering volume/track control for a JBL 56827, those wires are on a different harness slot that wasn't part of this package.This is the most expensive solution of the four I tried, but it is the only one that actually worked, and the results sound great and functions perfectly. I lost steering wheel volume control, but it sounds like for another $50 you can get a universal steering wheel control adapter. However I'm pretty much over this project, and I'm fine with turning the volume knob by hand. It is so much better having a modern headunit in place of the crappy JBL factory unit, the audio sounds much cleaner and more full despite not doing anything to the factory speakers yet.