BA31 & Display+ Installation

This page will guide you through installing the BA31 Bluetooth Retrofit Kit and the optional Display+ LCD module into a BMW CM5908 radio.

Step 1: Cassette Deck Removal

The first step is to remove the factory cassette deck from the radio. For this step, follow along with the video below until the cassette deck is removed from the radio (about 3:45 in).

Step 2: Mounting Tabs Transfer

Transfer the mounting tabs located near the back left and right of the cassette assembly to their respective corners on the BA31 board. Use the screws that come pre-installed in the board to secure the tabs.

Step 3: Front Panel Cable Removal (Display+ Only)

If installing a CM5908 Display+ kit, remove the copper-colored flex cable of the front panel from its connector underneath the cassette deck. First, slide the outer shell of the connector towards the rear of the radio to unlock it, then gently and evenly pull the cable towards the rear until it comes out.

Step 4: Bottom Flex Cable Install (Display+ Only)

Next, we'll install the large white flex cable included with the Display+ kit between the bottom of the BA31 board and the main radio board.

Start with the BA31 side. Ensure you have the cable oriented so that you can see the exposed metal ends as you insert it into the gray connector on the bottom of the BA31 board labeled "Front Panel OUT".

The cable takes a moderate force to insert, and it's OK to put a crease in the cable just behind the plastic backing strip to get enough leverage. Once inserted, straighten the crease back out.

Now take the other end of the cable and insert it into the open white connector on the radio board. Ensure the outer shell is still in the unlocked position when inserting.

Once inserted completely, pull the shell forwards to lock it in place.

Step 5: Board Install

Next, we'll install the BA31 board into the radio chassis. There are a number of items to get situated as this happens, so perform it in the following sub-steps:

  • Ensure all wire harnesses are clear of the area where the board will be inserted
  • Begin inserting the rear of the board down into place. Use a finger underneath the board to guide the white cassette flex connector up through the hole in the board
  • If installing the Display+, grab the loose copper flex cable underneath the board and bend it upwards so it's vertical
  • Lower the front edge of the board down into place, and if holding the copper flex, release it
  • Ensure all 3 mounting points are on top of their chassis bosses, then secure the board in place using screws removed from these 3 locations. Get all 3 started first then go back and tighten down

Step 6: Board Connections

Connect up all the electrical connections on the board:

  1. 5-pin harness at the rear left connects to "Main Power"
  2. 3-pin harness at front right connects to "Line Out"
  3. 8-pin harness removed from rear of volume board goes into "Volume OUT"
  4. Use the 8-pin harness included with kit to connect the volume board to the connector labeled "Volume IN"

  5. Insert the cassette flex cable into the locking white connector labeled "Main Cassette". Ensure the lock is released first by pulling the outer shell upward, then once the cable is inserted, push down simultaneously on the cable and shell to secure into place. There should be no visible metal of the cable leads once locked.

  6. (Display+ Only) Insert the copper flex into the gray connector labeled "Front Panel IN". Do this carefully and gently - excessive pulling will tear the cable at the tight U-bend. Once the cable is lined up in the connector slot, push forward firmly until it slides in.

  7. (Display+ Only) Install the short narrow flex cable included with the Display+ kit into its beige connector on the BA31 board labeled "Display+". The connector has a locking mechanism that must be pulled upward first to unlock. Be delicate - the throw of this locking mechanism is small compared to other locking shells we've encountered, only about 2mm. Once it's unlocked, insert one end of the flex cable with its exposed ends pointing towards the front of the radio until it bottoms out (which is also not that deep). Push both sides of the lock downward to lock into place. There will be a small amount of exposed leads on the cable when locked in place.

Step 7a: Reinstall LCD (Display+ Only)

If not done previously, remove the top and side screws securing the faceplate to the chassis. Pull the top edge of the faceplate outward just a bit to give more clearance.

Insert the Display+ module into the radio chassis in the reverse of the removal. Note that the connector on the bottom of Display+ that connects to the radio board has 1 fewer pin than the old unit. The physical size of the module should only allow it to fit in the correct orientation (with the unused, exposed pin on the right side of the radio). Line up the left edge of the connector and the receptacle and push down into place.

Insert the other end of the loose small flex cable into the connector on the rear of the Display+. This is an identical connector, so unlock it by pulling the tab toward the rear, insert the cable, then lock into place.

Step 7b: Reinstall LCD (Non-Display+ Only)

Reinsert the factory LCD module in the reverse order of removal.

Step 8: Install Mic/Aux Cable

The final harness to connect is the external mic/aux cable included with the kit. The 5-pin harness end attaches to the connector labeled "Ext. Mic/Aux" at the back right of the BA31 board. The cable will run out the rear of the radio between the heat sink and the rear chassis cover. We recommend tying a single knot in the cab to act as a strain relief at this exit point.

Step 9: Reinstall Top Lid

Ensure the mic/aux cable is properly routed in its channel, the reinstall the radio's top lid and screw into place.

The rest of reinstallation is the reverse of removal. Install the included microphone into the car and run the cable to behind the radio, then plug into the 1/8" jack labeled "MIC".