Success and failure.

Well, last weekend I pulled out the AUX and iPod jacks from my car and went to work adapting proper connections on the ends for standard car head units – namely a 3.5mm plug for the AUX and USB for the iPod/other USB devices.
The 2009 Scion tC has its iPod and AUX wiring done differently from most other (previous) Toyota/Scion vehicles. The standard connection at the head unit that the AUX comes in does not exist, you only have the iPod HU plug and the one used for the speed-controlled volume and steering wheel control.
This necessitates all new wiring.

Outside their natural habitat

Outside their natural habitat

The iPod/AUX connector on the other side.

The iPod/AUX connector on the other side.

Connector's not helpful, wires are!

Connector’s not helpful, wires are!

Continuity tests give me this info for the AUX

Continuity tests give me this info for the AUX

Soldered and heatshrunk, nice and neat.

Soldered and heatshrunk, nice and neat.

The stock iPod cable.

The stock iPod cable.

Dangers of being careless with sharp objects.

Dangers of being careless with sharp objects.

Everything together!

Everything together!

USB!

USB!

Using original port.

Using original port.

I didn’t show the iPod/USB wiring because there were a ton of wires, and I was basically picking them at random (after matching the cable to the harness via continuity testing)
What I missed however, was measuring the impedance on the wires I used, because plugging the iPod in via USB this way didn’t work at all. Wouldn’t even charge.
The reason for this I think is because Apple sets up different connection modes for charging and control by using specific resistances on certain lines. The original Scion iPod cable doesn’t use USB for communication, it goes directly to the stock head unit, and I fear that these resistance values are in place inside that large grey plug. Having these values in place on the USB connection is preventing the iPod from entering its appropriate accessory mode (as the stock USB connection on my Kenwood deck also seems to have some in place itself), although it doesn’t seem to hamper other USB devices.

The AUX port works brilliantly, however.

I may at some point in the future revisit this,  and try to find unimpeded (see what I did there) wires on the plug to use, and try wiring the USB through that.
Dealing with USB cables is quite a pain however, as they’re sensitive to interference, and by doing this you’re breaking the shielding on the cable for a small length.

For now, I’ve just run the USB from the back of my Kenwood unit through to the hole where the iPod jack was in the center console – it just reaches, and have my iPod plugged directly in there. Same basic result as I was going for to begin with.

Hope this is informational for some, at least on the scionlife.com forums!

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