Adding AUX Input to Volvo 740/760/940/960 CR-8xx Series Headunits

2021.09.14 | Yuki Rea

The CR-8xx headunits came equipped in some Volvo 700 and 900 series models from the 1980s and 90s. This is a fairly basic headunit with analog volume, fader, treble, and bass controls. This basic analog processing makes this headunit extremely easy to modify. There are no electronics needed, just an audio cable and soldering skills. The CR-8xx series headunits also power the amplifier regardless of if you have the correct anti-theft code entered into the radio making this mod work at all times as long as the unit has power. This modification was preformed on a Volvo CR-814 but may also work on other CR-800 series units.


Requirements for this modification

  1. Soldering iron
  2. Phillips/Plus screwdriver
  3. Audio cable of your choice

Optional recommended tools

  1. Lab bench power supply
  2. Solder wick and/or solder sucker
  3. Wire stripper
  4. Flush cutter
  5. Speakers for testing

Disassembly

In order to preform this modification you will first need to extract the head unit from your car if you have not done so already. The volume and tuner knobs need to be removed in order to access the clips that hold in the headunit. The rubber knobs, and plastic knobs they sit in can be pulled straight off the potentiometers. Once the knobs are removed you should be able to see a metal clip inside the holes left by the knobs. Pull these tabs towards the inside of the headunit with small screwdrivers to unlock the headunit. Pull the headunit out while holding both tabs in at the same time. Once you have the headunit out of the car, take out all of the phillips/plus screws that hold on the top cover. Only the top cover will need to be removed for this modification.


Modification

This modification is very simple, an audio cable only needs to be soldered onto the correct pins on the PCB. Connect the left channel to LI pin, right channel to RI, and ground to GND as shown in the photos below. Soldering the cable here allows you to still retain treble, bass, fader, and volume control but bypass any digital input switching circuitry. The AUX input will be active at all times, you can overlay the AUX input on top of radio, cassette, and CD. It will also work if you do not have the anti-theft code entered. You can add a 3.5mm jack inside the case or route the cable out the rear of the headunit and under your dash to the location of your choice.

[ black wire = Left channel LI | red wire = Right channel RI | white wire = ground GND ]