"Dan, to turn your 20 into ele
"Dan, to turn your 20 into electric start, you can first check the flywheel. If it has gear teeth around the outside then the allowance to convert is there. If not, in addition to other items you will need a "ring gear" from Merc (about 40 bucks).
Additionally, you will need a starter (ones in the aftermarket are cheaper - around 100 bucks) additionally, you will need a starter solenoid, some cables (to connect to the battery) and a battery.
You will also require a "remote attaching kit" to change from tiller to allow connection of the control cables.
Depending on your model/year it may or may not already have a charging stator with the leads simply going to a isolator block. If so, the addition of a rectifier will allow you to recharge the battery through the motor itself. If not you have decide if you would like that feature (adds upwards of 200 bucks to the conversion).
If your old Force controls are a US Marine shifter, it can be adapted for use on the Merc. The shifter will be set-up currently to retract the cables (make them shorter) to operate the shift/throttle on the Force - Merc's work opposite, but the shifter has a large cam that can be reversed to accomplish this (assuming a US Marine control). Additionally, those controls have clearly marked "connection points" for Force/Merc and OMC motors. It does however require some disassembly/reassembly to accomplish this.
Also, if you want to use your existing cables, you will need to change the ends (at the motor end) - they connect up different. If you have generic (3300 or 33C morse cables) the adapter ends for Merc are available from most marine parts places for about 15 bucks...
If you post your serial/model number, I can post the Merc part numbers for you which can then be cross referenced to aftermarket parts, although some items will have to come from Merc...."