1. Disconnect from power and unscrew the screws on the bottom cover. 
2. Carefully turn over and remove the top cover
3. Remove the PCB (controller board) taking particular care not to damage the fragile connector coming from the flux-gate compass.
4. Inspect and if needed replace any broken gears, belts etc
5. The shaft output bearing / seal housing is available from printables.com (see next step) if you can't find an original part.

Visit https://www.printables.com/model/570906-raymarine-st1000-tiller-autopilot-limit-switch-car/files
and download the switch bracket .stl file. This can then be printed with 15% infill or higher recommended. 0.32mm layer height is fine but 0,2 looks better. For strength 4 layers of top / bottom and sides recommended. Skirt with tree supports touching build plate should be fine. It should fit snugly over the screw pillars in the base of the tiller auto pilot and lie flush with the top of the pillars when pressed into place. Note that the bottom edges of the pillar posts can be a bit ragged but that is purely cosmetic.

Insert the spring into its 'garage' on the face of the switch carrier and make sure it doesn't fall out while you fix the micro switch to hold it in place.

The inboard switch should have had its wheel snipped off if it had one. It must be mounted facing up, lever towards the middle of the 3D printed unit, locking the spring into place.

Screw the two micro switches into place using m2.5 x 14mm screws. The outboard facing switch has to have a wheel and it should point toward the top motor side.

The actuator wire should be a stainless type. Mine was made from a single 316l stainless welding wire of approx. 1.5mm. TIG wire or a welding stick with the shield stripped off will do. Any comparable wire will also work as long as it is strong enough to stand some abuse. Ask a friendly neighborhood welder, he probably won't even charge you for it.

See the files section for a .pdf file of the dimensions.

Micro switches will have three lugs. One labelled C (common), one labelled NO (Normally Open) and one labelled NC (Normally closed). This project only needs the C and the NC lugs. Remove the center lug (labelled NO) to make room for the diode.

For best results try to bend them so they are a friction fit on the two remaining switch lugs, this helps with soldering. Position the diodes in such a way that the stripes on them are facing each other. The one on the side of the spring needs to lay flat against the plastic. The one under the switch with the roller should be bent forward and not stuck down under the unit where it will interfere with the fit (this bend can also be done after soldering if the U is left long enough)

It helps to pre-tin every part before you attempt to connect it. This makes it faster and you have less chance of a bad solder joint.

The diodes should have been soldered into the lugs already, now add a wire to the two lugs where the diode's stripes are located. Make sure to add new solder and use enough heat that the wire is not just sticking superficially but properly soldered.

The switch with the roller (outboard side) now needs to get a wire that goes to the motor. You can either solder a short piece of wire onto this lug with a spade connector (M) male to mate with the motor wire's spade (F) female or cut off the motor wire's spade (leave about 5 cm, 2" of wire) and solder the motor wire directly to the switch (and diode). If you choose to cut and solder the motor wire be careful of the wire routing, it must not prevent you from mounting the unit when you are finished soldering. If you opted to connect a new spade to the motor wire leave this new wire short, you don't want it to go astray and get chafed on the mechanism.