I'm not positive I know what you mean by tension on/off. Should I release the cable from the anchor bolt? Or do you just mean shifted into loose/tight cable position?

Here is what I just did: in smallest cog and inner ring I took all tension off (clicked shifter behind lever in), cable goes slack on downtube.

Then pushed the lever in to shift to outer ring. Hear 3 clicks, goes onto big ring, falls off when I release it. Now it sits on the inner ring, with plenty of tension on the cable on the downtube. If I push the lever again it doesn't make any clicks.

*RE: 3 clicks...these are a pair of used 105s (I buggered my right one by not knowing I need to be in my lowest gear to get the cable out to replace...I know, stupidest bike-related mistake I've ever made). Seller said he had both a triple and a double. Could I have gotten a triple, despite requesting a double? Any way to check? I still have the old shifters and the left worked, so I guess I could re-install it. But if I could check without undoing cables, brake, hoods, shifters, that would be nice.