I have a 2007 Accord with a 2.4L engine, which has a factory radio installed (6CD changer, premium sound system, dual climate control). I am now looking at ways to upgrade / extend it for MP3 / FLAC music playback.

My current plan is to install a Pioneer head unit in the lower dash compartment and connect it to the Line-in (CDC) input of the factory radio. What I would like to do is to remote control both my Pioneer unit and the factory radio from the steering wheel.

Is it possible to split the signals coming from the steering wheel between the factory head unit and the pioneer head unit?
I understand that I need an adapter for converting Honda-specific signals to Pioneer-specific signals using a unit similar to this: But as the steering wheel controls communicate by setting different resistance levels, a simple Y-cable is not likely to work.
Is there a 'signal repeater' or any other device which I could use for this purpose?

Alternatively, is there an adapter which plugs into the Factory Radio's CD-Changer connector and outputs Remote Control signals for the Pioneer unit?

 

You can do what you want. You will need to add a switch and relay(s) that changes where the steering wheel controls route to, you cannot wire them in parallel to both the stock HU and the interface.



To do this, simply identify your steering wheel remote wires and route them through a 5-pin relay (one for each wire). the N.C. position would be to the stock HU and the N.O. position would be for the interface. The switch would control power to the relay coil (you'll need a 12V source and ground).



To automate the process, you could power the relays off the aftermarket HU remote output so anytime the aftermarket HU is on, the relays switch to route steering controls there.



The issue you'll have will be with cascading volume controls. Meaning that your stock HU volume control will always affect the sound level and the aftermarket HU volume control (when using that as a source) will only act as attenuation of the stock volume level. you also need to be careful to not over-drive the AUX input. Figure that most AUX inputs can only handle 1.2V or so, which means a 4V aftermarket HU will start clipping around 30% volume. Ideally, you'd only use the stock volume control and leave the aftermarket fixed.



The alternate process is to route the factory radio through the aftermarket radio (something I do on my 2014). for this you add a LOC which converts the front speaker outputs from the factory radio into RCA and feeds that into the aftermarket HU AUX input. Then you are always routing through the aftermarket HU which adds the benefit of sound shaping tools (such as EQ, Time Alignment, Crossovers, etc.). In this case you'd still want the steering wheel control switch (if desired) but you wouldn't be able to automate it.



Neither process is very complicated or expensive, but consider the impacts of cascading volume controls and report back with your decision.



Cheers!

 

Thanks for all the explanation. The cascading volume control issue sounds really bad, that is probably a show-stopper. It seems likely that I'll go for the other option and use the aftermarket as the main unit.

 

The cascading volume control side-effect isn't a deal breaker. it just requires you pay attention. i've had it for 3 years after adding an aftermarket in a lower pocked while keeping the stock (because the 2013+ have an integrated HU). I run the stock through the aftermarket system. I have a video of this setup here: