It's been years since I have messed around with small parts and procedures (macular degeneration and Glaucoma) but my recollection is that it is simply not nearly as hard as the o.p. is making it. The derailleur end of the cable needs to be perfect with no frayed strands whatsoever. Period. A new cable will be that way. Is o.p. using an old cable? You poke the end of the cable without the cable stop into whatever hole is indicated by the manufacturer, and pull the cable through till it stops. The shifter must be in the appropriate gear specified by the manufacturer. Getting the indexing right, is MUCH harder to get right, and if the o.p. is having this much trouble just getting the shift cable installed they should simply quit while they are ahead. A bike co-op will charge a pittance to do this or may not charge at all! Recommended.