If you follow the diagram you will have a far better understanding of how it all works. If your using different coloured wire to the diagram make a note of it. Good luck, its easier than you think.
A basicgood understanding of mechanics would help save garage bills. Sure someone will correct me but insurance may be higher on a 109 if it is registered as having seats in the back.
Welcome. Come and join us series III owners. Don't worry about homework, to late for that, just get yourself a Haynes manual and the forum will do the rest.