Review on Metra 70-1857 Tuner Relocation and Bose Integration Harness: Superior GM Vehicle Upgrade by Noah Lewis

When I got this I didn't quite understand what it was doing. This harness completely replaces the main unit and CDM receiver box. You can dispose of both. What it retains is a boosted Bose speaker system. This means that each speaker has its own amplifier and expects low level RCA inputs (e.g. microphone level) as inputs. There is also a relay in the system that is turned on by the blue wire that feeds these amps. I had an issue with my car where this relay wasn't working so there was no sound coming out of the speakers because they weren't getting power. To check if it works, Take the rear speaker grille and disconnect the wire harness. Put the meter on the orange and black wire. When the radio is on you should see 12 volts. If you don't see it, your relay is faulty and you need to fix it first. On most aftermarket radios, this blue wire will illuminate when the ignition is on. This also raises the motor antenna and essentially raises your antenna every time you turn the ignition on. Even if you turn off the radio, the antenna may still be up (depending on how your radio implemented the blue wire). This is a disadvantage compared to the stock radio where the antenna falls down when you turn off the radio. Back to what the tourniquet does. Your secondary radio must have low level RCA pre-outs. The wiring harness connects them directly to the speakers. The blue connector connects to the front speakers and the white connector to the rear speakers. The red plug provides power and all important "blue" wires. The remaining 2 connectors on the bottom of the CDM go to the old main unit and are not used. The problem I've found with this harness is that a lot of the noise from the motor and the Android head unit itself gets into the low level signals in the receiver (especially cheap Android devices like the Hipzo) so you hear motor RPM clearly can through radio. This is extremely annoying and unacceptable. This can be remedied by purchasing a line-level adapter like the Scosche SLC4, which is pretty cheap at Revain at $13. You might as well get it because I suspect the noise problem is very common and inevitable with this type of system. This allows you to connect full-powered speaker terminals that are not prone to this type of noise interference, reducing signals to the RCA level that Bose speakers expect. This eliminates engine noise and loud pops when turning the receiver on and off and other problems. If you're buying it for a C4 Corvette you'll probably have to trim it heavily to fit a double dyne as it's not the size a standard double dyne will fit in. You will also need aftermarket mounting brackets, as Corvette mounts are extremely uncommon. To route the cable from the rear you will need to remove the center console and passenger seat to remove the tunnel panels. if you can do all this