Did he leave out the 2 rectifiers (i.e. diodes)? If he did, they need to be installed to make your electrical system work properly. I can tell you how to make it half-work without them, but that is just making a trap for the next person to work on the mower. I suggest you show the sparky the wiring diagram I posted above, and ask him to put it back the way it should be rather than screwing up your mower. Then, after he's fixed it, never go back to him.
