ADDED THE PICS BACK AGAIN AND VIDEO [HOSTED BY FORUM, should they shouldn't disappear]
I'll try piecing together a DIY on how I modified my Becker Grand Prix 780 headunit (HU) to accept an auxiliary input (ipod for me). I started with a Becker HU I grabbed from a '89 420SEL at our shop. The first thing I did was verify it was working before proceeding. The HU does not require a CODE, but it features an 'anti-theft' wiring scheme.
I grabbed the above picture off another site, the 'anti-theft' feature is the wiring connected to the flat five-pin connector (#9, centered) and the three-prong copper connector (#10, center-bottom). To bypass the 'anti-theft' feature, all that needs to be done is connect ALL the wires out of the flat five-pin connector TO the three-prong copper connector (which is a ground). In essence, you are grounding all the wires in the flat five-pin connector.
There a many ways to do it, such as: use the existing anti-theft harness, tie all the leads together and connect them to the spade connector (w/spring clip) that goes on the three-prong connector.
However, I simply desoldered the wires from the inside of the anti-theft connector (blue arrow), tied them together and soldered them to the wire coming from the three-prong connector (red arrow) all inside the HU. You can see the thin/thick brown wires leading down towards the three-prong connector, that's what I soldered together.
Now this will prevent the HU from locking when used in another vehicle w/o the 'anti-theft' feature or it allows one to bypass it. Just note that if your HU is already locked, then I believe you need to go to the dealer to get it unlocked. As long as the HU is removed from the car w/o the alarm activated, the HU won't be locked.
*IMPORTANT*, the 'anti-theft' feature needs to be bypassed or connected (to a working OE alarm) before powering the HU, or it'll lock.
Here is my "testing" setup:
^ Becker HU, iPod Mini (auxiliary source), and HK (BMW) speakers
