I have a Haynes manual for the 124 series, and would not pay for it again. There were several versions of the six-cylinder engine and at least two V8s in US models, plus several versions of a two-liter four sold in Europe. Considering the many engines to be covered, Haynes provides only sketchy information on a few of them and mentions the varying modifications only with vague generalities.
Electrical diagrams are provided for several 124 models and I have been unable to find that any of them gives a reliable diagram for my car.
If anyone wants a Haynes 124 manual, you may borrow mine for the cost of two-way shipping, and if I don't get it back, I'll live somehow. It would be worth seeing what is in this book before you buy it, because I have not opened it since I bought the CD set. If there is a better book available, I would love to know about it. Amateur wrenches need all the information they can get.
I understand some well-equipped folks are making the CDs available to friends, etc.
Note: FWIW my Haynes manual is a slick paperback with 191 marked pages. "First published 1994 in Germany by Delius, Klassing & Co."