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First thing to do is remove the switch housing from the mower handle is by unscrewing two screws at the bottom. *** You should be able to just pull this bottom piece off and then push the housing off the handle, before twisting in 90 degrees to remove it from the control bar. *** With the switch housing loose, unscrew the three screws to get to the switch inside. *** Take those three screws out you can just remove this half of the housing and pop that to one side - inside we have the on/off switch. It's very important to take note of how the cables are laid out in the housing - if necessary you might want to take a photo to remind yourself. *** The cables are attached on both sides of the switch, through push-fit connections and they're very tightly held in place inside the switch with small barbs so you're going to need to, very gently, but firmly take a pair of pliers and pull those wires out of the switch. If you happen to damage the wires while you're doing this, you can always strip them back before reinserting them back into your switch. *** With the wires out of the old switch, just replace them with the new one. Once you put the wires back into the switch, it's a really good idea to just give each one a little pull to check that it's really locked in place by the barb. *** Replace the new switch back into the housing. *** With that done, reattached it to the mower handle.
If you have any questions, please let me know. I wish you the best.