There are different Docks....
However, I have one of the first Docks that came out.
Sound works but the video out may not work the same.
Which Dock do you have?
1. iPod Universal Dock MA045G/A (Note this is called iPod Universal Dock and is the older version)
2. Apple Universal Dock (This is the newer model)
http://store.apple.com/us/product/MC746LL/A?mco=MTY3ODQ5OTY
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As far as the Dock Adapters themselves, here are the numbers.
#3 - iPod mini and iPod mini 2nd generation
#4 - iPod 20GB, U2 Special Edition
#5 - iPod 40GB
#6 - iPod with color display, 20GB, 30GB, U2 Special Edition
#7 - iPod with color display, 40GB, 60GB
#8 - iPod nano
#9 - iPod classic 80GB, 120GB, 160GB (Late 2009), iPod 5th generation 30GB
#10 - iPod classic 160GB, iPod 5th generation 60GB and 80GB (Late 2006)
#11 - iPod nano 2nd generation
#12 - iPhone 1st generation
#13 - iPod Nano 3rd generation
#14 - iPod Touch 1st generation
#15 - iPhone 3G, 3GS
#16 - iPod Touch 2nd, 3rd generation
#17 - iPod nano 4th generation
#18 - iPod nano 5th generation
#19 - iPhone 4
#20 - iPod Touch 4th generation
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You would need a #20 for the 4th generation iPod Touch and a #16 for the 2nd and 3rd generation iPod Touch.
Here are the Dock Adapters for the 4th generation.
http://store.apple.com/us/product/MC650ZM/A?fnode=MTY1NDA0OQ&mco=MTg5MTgxMjc