..turned into a right mess.
Background: Bent rear mech. Mechanic advised beyond repair, so I thought I'd replace it myself - how hard can it be?!
4 days later the new rear mech arrived and I successfully took the old one off and put the new one on in only about 15min.
But then I managed to slightly unwind the old cable and it fouled, so had to buy a new cable.. and some new end caps and some cable cutters. Waited another 4 days.
Fitting the new cable into the shifter pod the insides all came apart. Then I lost one bit (in the grass), but after an hour of frustration decided that some of the internals weren't really necessary as they were just "gear indication". Put it all back together after about another hour of experimentation only to discover that it now doesn't "click" down properly.
Next step: New shifter.
In summary: Initially required one rear mech and 5min installation time.
By the time I'd had a go the shopping list was: Rear mech, cables, caps and cutters, a new shifter and 3.5 hours of wasted effort.
It would have been a lot quicker and cheaper to just take it to a shop!