I came up with a cheap, workable, solution that meets my needs well enough thus far. I figure I should update my post with what I'm doing in case anyone else is looking for a passable solution.
Prior to even making this post, I had ordered three different super cheap chinese bluetooth ipod adapters on eBay. Two of them never mentioned anything about working with car stereos, and neither of those options worked at all. They were more intended for using Bluetooth to extend the range of an iPod dock. However, one of the three did have some photos suggesting the device could be plugged into the USB port of a car, that one appears to be the ticket!
When connected to the USB port, it presents to the truck as a storage device with MP3s on it. However it apparently transcodes any Bluetooth audio sent to it to MP3 and sends it to the truck stereo. Sadly, it doesn't present any media information (track name/artist/album) on the screen; however it does correctly translate the next/prev tracks to the appropriate Bluetooth AVRCP commands, which Spotify honors perfectly! I'm much more interested in the next/prev track controls than the media information, so this is definitely something I can live with.
Also, I was able to retain the Bluetooth connection to the truck itself for phone use.
- eBay item I purchased. I included a pic from their eBay listing in the album below in case the eBay listing is no longer valid. It set me back a whopping $2.99 shipped - though shipping did take almost 3 weeks.
Steps for success. (I'm using a Google Nexus 6p, but should be essentially the same for any Android device)
- Your phone has already been paired to your truck's Bluetooth (assuming you want to use the truck's hands-free phone capabilities).
- Start your truck, listen to music from some audio source (XM, AM/FM, CD)
- Plug the dongle in. Truck will detect is as a thumb drive of MP3s and begin "playing" it. However it will be silent as you are not currently streaming to the dongle.
- Pair your phone to the USB dongle. You only want to select "Media audio" as the purpose of the pairing. Do not check "phone audio" or "contact sharing." If there are no check boxes during the pairing process on your phone, you can probably find them by editing the pairing for the dongle after you actually create the connection. Also, check the pairing settings for the truck, make sure you are only using the truck pairing for "phone audio" and "contact sharing."
- Begin playing audio on your phone (MP3s, Spotify, Pandora, etc). You should hear the audio playing on your truck Stereo.
- The next/prev track controls on your steering wheel and on the head unit should be fully functional!
For the least headaches, I've found that it's best (most reliable) to unplug the dongle after turning the truck off. When I get in the truck I start it, let my phone pair to the truck (for phone calls), then connect the dongle. My phone automatically pairs to it for media purposes and stays connected to the truck for phone calls.
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