So I'd like to hook up an auxiliary input to my stock 95 Honda Accord head unit, via the MBUS connector (used for an add-on Alpine 6 disk cd changer) on the back of the head unit.

The problem is emulating a cd player, so it can go into AUX mode.

Since my add-on Alpine changer won't read disks any more (head unit still works fine), can I just splice into the R/L channel lines of the MBUS cable and connect to my IPOD? I'm assuming it will still go into AUX mode since the changer is still present.

MBUS pin out:

 

Probably.

I'd cut the L and R wires, and tap the SIG GND line.

 

What do you tap the SIG GND to? I'm assuming another ground, but from where?

 

I did something similar using the IPBUS input on a Pioneer head unit I had. Run the ground to the ground that will be coming out of the Ipod. If the volume is too low, even with the Ipod turned all the way up, get a battery-powered headphone amplifier from the shack. I had to do that.

 

This is going to sound stupid, but where is the ground that comes out of the Ipod? I'm using a Y cable (2 RCA plugs to a mini jack) cable. I'm assuming there's a ground, but where is it on the Y cable?

 

I believe the ground would be common between the 2 RCA jacks. It would be the outer "ring" on them.
On mine, I just cut the end off a 1/8th to 1/8th cable, it had 3 wires coming out of it. IIRC, ground would have continuity with postion 1 on those plugs in the picture.

 

On each of the two RCA cables, you have a tip (center) and a sleeve (outer). The two tips are right and left. The two sleeves are both ground.

Alternately, you can forgo this RCA business and just use a 1/8" plug. See here for TRS pinout. Follow the right-most column under "stereo".

Tip = Left
Ring = Right
Sleeve = GND.

 

Thanks to both of you.

 

One more question, what do you think is signaling the head unit that there is an aux. connected? In other words, how can I emulate a cd changer w/ no changer actually there?

 

No idea. My guess would be that they communicate over the data bus line.

Obtain a serial data analyzer, capture and analyze the datastream that passes between the two devices, learn assembly, build and program a microcontroller to emulate that communication, connect it to the data bus, profit.