This WILL NOT play through my car speakers.

maybe when you plugged the cord into the speakers two days ago maybe you pressed to hard in the hole so maybe you broke it

These instructions is direct from "Belkin" website.

-Glenn

update your firmware or reset the i pod it will solve your problem

Check the pins on the speaker and on the plugin on the iPod, that's the problem usually. Also, check if the iPod is truly compatible, even if it worked before it may not be. I have seen car chargers for say a 2G iPhone work for a bit then say incompatible, it happens. Here are the compatible iPods for the iM310:

Plays and charges
iPod mini;
iPod nano 1G, 2G, 3G, 4G;
iPod classic 3G, 4G, 5G, 5.5G, 6G;
iPod touch 1G, 2G

Good luck!
EJ

the iphone has only one speaker located at the left side, what you see on the opposite side is the microphone. this mean, your iphone is in proper condition and the speaker is working perfectly. nothing to worry about...
For more iPhone / iPod touch tips, visit my blog.

...

Just solved exactly the same problem by powering off and on the iPhone

When the OnStage speakers first came out, the charger was not compatible with 3g iPods or iPhones. Newer speakers have an upgraded charger and will charge all current iPods/iPhones (up to and including iPhone 3Gs)

Bad news is that there's no way to upgrade an old OnStage.

You can test yours by trying an iPhone 3G (if you have a friend with one, for example) to see if you have the old or the new charging circuit.

Look at:
http://www.speakerstation.co.uk/ipod-speaker-docks-ct-87.html

"...
Important Note: iPods released since Sept 2008 (e.g. Touch 2nd Gen, 4th Gen iPod Nano and iPod Classic 120 Gigabyte, iPhone 3g and onwards) have an updated dock connector that means older revisions of speaker dock may not be able to charge these newer models of iPod/iPhone. Older docks should play music from these newer models with no problem.
The problem with charging is due to Apple removing support for 12v (firewire) charging on these new models of iPod/iPhone. Only 5v (USB) charging is supported on these new models.
..."

Keep the home and power button pressed for 10 seconds, then, leave power and keep the home button pressed...shud be able to see the charging cable logo...then restore it...

Dude, change the station in your car to match the station on the tune cast doodad. 
Or: Go to BestBuy. Purchase a new one. Save the receipt. Go sit in your car and make sure the new one works. Then take the old one and put in back in the package and take the receipt with it, up to the return counter and tell whoever that it didn't work and you'd just like your money back. :) That's what my friend told me to do. And I would never do that.