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Notes on MOST bridge adapters / loopback connectors for Audi cars with MMI (e.g. Audi A6)

14.7.2008 - The Audi MMI (the full system as found in A6/A8/Q7 and factory navigation equipped A4 B8 and A5) is based on a MOST fiber-optic loop or ring connecting the various components (radio, telephone, navigation, amplifier etc.) that make up the system. In the MOST ring each component is connected to a dual MOST connector with an inbound fiber-optic cable and an outbound fiber-optic cable.

Since each component is thus an integral part of the MOST ring (the ring goes "through" each component), removing even one component from the ring will leave the ring broken and all components of the MMI system will stop working. Basically you loose radio, navigation, telephone functions - they all just go blank until the ring is complete again. But sometimes during installations and repairs you may need to remove some component of the MMI system and still use the rest of the system.

To be able to remove MMI components and still use the system without rewiring things, the MOST ring has to be patched. The most elegant solution for this is the use of a MOST bridge adapter or a "flat connector housing with fibre optic bridge" as Audi calls it, that just plugs into the empty MOST connector and patches the ring for as long as is necessary - and is then easily removed when not needed anymore.

This part is available from Tyco Electronics as part number 1-1452102-1 or 1452102 short. Apparently Audi sells and uses this same part with the Audi part number 4E0 973 802, which you can order from your dealer. Audi for example ships some cars (at least in the U.S.) pre-wired for navigation or satellite radio installation that have these MOST bridge adapters in place of the missing pre-wired components. Kufatec.de should also be able to sell you this component if you email for an "Audi MOST bridge adapter".

Photobucket.com album with pictures of my MOST bridge adapter:
http://s77.photobucket.com/albums/j62/mlk_05/MOST%20bridge%20connector/

Some alternative solutions have also been proposed...

Etadyne sells a MOST loopback connector (part 4040) that requires more work to do the trick, but should work too:
http://www.etadyne.com/product-mostloop.htm
http://www.etadyne.com/DIYmost.htm

On navplus.us Dalep also suggested that ends of two MOST cables can just be pointed towards each other and tied together with a bit of tape or heat shrink tubing since apparently the MOST fiber alignment is very non precise.

Navplus.us thread for the original information these notes are based on, thanks all for the info:
MOST fiber-optic bender? - http://www.navplus.us/forums/showthread.php?t=8963

Tyco Electronics provides schematics of their parts for those with accounts to their site (see part number 1452102):
http://www.tycoelectronicsmost.com/Customer-Drawings.customer-drawings.0.html

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