I have a set of these downtube indexed shifters and I question whether the left (front derailleur) one is installed and working as it should. I haven't been able to find any instructions on how to install these: the closest I've found is for the model 7800 shifters. First of all how does the circular piece that goes over the brazed on downtube boss get oriented? Then how is the shifter supposed to be oriented over that because I've found there is only one way that it will key together. I have installed it so that the large tab on the flat surface of the circular ring faces towards the bottom bracket; then when I install the shifter it keys in so the shifter has no forward stop, but it stops when you pull the shifter down quite a ways which seems backwards to me, although it allows you to be able to shift the deraileur. The instructions for the 7800 downtube shifters say to orient the large tab toward the head tube which I can't get to work at all. It's almost like the mechanism inside the shifter got turned around somehow; either that or this shifter is supposed to work without an upper stop.

Thanks for any help.