Howdy, Alabass.
Welcome to iboats.
My guess is that he inadvertently grounded the ignition through the tach or pulled the kill switch, which disables the ignition.
Go to Engine FAQs, "Outboard won't start" and do the troubleshooting. It may not show you what is wrong, but it will eliminate several possibilities.
If that does no good, disconnect the tach completely and go to the wiring diagram in the Service Manual.
No Service Manual? Thought so. Have him get one. As well as showing him which wires go where it will caution him to never work on the electrical stuff with the battery connected.
Good luck, and let us know how it turns out.