Just purchased a 2001 RK with the adjustable backrest. There is no tension on the cable so something is not working as it should but I don't know how the cable should be set up. When I pull the lever under the left side of the seat, the cable moves but since it is loose, it does nothing. Any help would be appreciated.
You can see in the pic that the cable is curved where it is supposed to be held in position. There is no tension on the cable at all so it falls off of the arm where it should clip.

 

Is the cable attached at the other end where the handle is? Also, you can confirm if the thing works right just by bypassing the cable and squeezing that lever with probably a pair of channel locks to make sure the mechanism works right. if it does, then it’s just a matter of figuring out the cable. My guess is that slack means it’s disconnected from the other end

 

Instruction sheet shows pics of how the cable should be attached, etc.

 

The cable sheath probably popped out of its holder on the lever under the seat. (The part that holds the sheath back when you squeeze the lever) It happens to mine occasionally.

 

I'm logged in to the serviceinfo site but cannot access the document.

 

I looked at it again and the cable is attached on the adjustment lever on the left side by the seat.
The "retainer" piece that the cable clips into on the backrest bracket is loose and can just slide out; there is no tension on it. When I manually move the pneumatic cylinder it goes up and down easily but doesn't stay in place at all. I have searched for information on this but not having any luck figuring out what's wrong

 

If the cable is loose, it's screwed up somewhere, regardless, the gas strut is probably blown if it moves freely.
With the cable loose and not pulling on the little lever at the end of the strut the strut should not move - it should be stationary. When you pull the lever it allows the strut to move.

Good thing these things are pretty cheap these days (cause China). Here is the full kit that should fit your bike if you just remove the little secondary bracket at the front of the mount:

https://www.ebay.com/itm/40527340808...3ABFBMhKXOiZtm

Here's the strut all by itself if that's all you want:

https://www.ebay.com/itm/33551821988...3ABFBMhKXOiZtm

 

Remove the hydraulic cylinder. Using finger pressure, press down on the actuator.

When you remove your finger, the actuator should extend.

The extended actuator maintains cable tension.

 

Thanks for the info! I'll check the cylinder and the links to parts.

 

I can move the strut up and down ... it does require quite a bit of pressure ... but it's definitely not stationary. I'll pull it apart and check it.