BMW Z3 Radio Head Unit Removal and Replacement
Article written and submitted by forum member ‘GazHyde’

In this case I am replacing the standard low quality OEM Business RDS head unit for a Sony MEX BT3800U head unit. This new unit provides better sound quality, and a host of extra features such as – Bluetooth Audio and Hands Free Phone, USB Socket, Auxiliary Line In socket and so on.

Difficulty rating 3/10 – It’s a couple of screws and plug and play wiring connectors. You don’t need to cut any wires, or solder anything. You do need to be careful that you don’t trap or damage any existing wiring!

Time Taken – 30 minutes

Tools/Parts Required

  • ISO Connector/Convertor to allow a non BMW head unit to be fitted. Mine cost about £10 from eBay.
  • set of small hex/allen keys
  • Flat blade screwdriver
The Procedure
1. Carefully prise open the two small flaps (circled in red) to reveal the two retaining screws.

2. Insert the allen key in to the screw head and undo both

3. Slowly and carefully pull the head unit forward. There isn’t much to grip, but I gently pulled with a finger in the cassette slot. If it doesn’t move, then you probably haven’t completely unscrewed both sides.

4. With the head unit tilted downwards you will see the connectors you need to unplug. The aerial connector pulls off, but the main wiring harness needs some effort to remove. There are instructions on the main harness connector block which explains how to remove it. Be careful!

This is a close up shot of both connectors for reference.

5. Attach the ISO Connector to the cars wiring loom. Make sure that you align the connectors correctly, as they will only fit in one correct combination! You can also see that I have fitted the Sony head unit cradle to the radio aperture.

The assembled wiring loom ready for the Sony MEX BT3800U Head unit

6. Connect the converted wiring harness and aerial connectors to the back of the head unit. The Sony unit has additional wire on the back which you probably won’t be using.

Carefully push all the wiring in to the dash aperture, and make sure it’s tucked neatly in. You can then start to push the head unit in to the cradle. Don’t force it if it doesn’t go fully in, you have most likely fouled the wiring behind the dash board. Remove the head unit, and recheck the wiring is out of the way.

Before fully inserting the unit it is sensible to test it first. I powered the unit on and checked the radio signal, and that a CD could be played.

When you are happy it’s functional, push the head unit back until it clicks in to the cradle. Fit the surround bezel and the control facia. Turn it on and make sure all the functions are working.