I finally soldered everything together and tested the tuner today, and it appears to work properly. I just have a few questions that weren't answered in the FAQ or at www.pcats.co.uk:

What is the female 3.5 mm stereo plug used for? Is it currently utilized in Hijack or the empeg car software?

There is an extra wire in the tuner plug which comes from the sled. It is violet and appears to be inserted into pin 7, but there is no matching wire in the plug for the PCA tuner. What purpose does it serve when used with the original tuner module?

Can I use the Sony stalk with the PCA tuner? There is no connector supplied for it in the kit, but there are a few pin headers that are apparently unused.

All in all, I would say that the kit was much easier to assemble than expected. Thanks for the hard work, Patrick.

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Can I use the Sony stalk with the PCA tuner?

Quote:
What is the female 3.5 mm stereo plug used for?

I believe you've found your stalk connector...

Thanks, I read through the relevant sections of the FAQ, but the actual plug for the Sony stalk isn't shown anywhere (not even in the section you cited). After I posted, I found the image listed at http://www.discountcarstereo.com/images/sony/jack.jpg and suddenly realized I had answered my own question.