I repaired this unit on my 82 242 . It took a look at the green book I got from Volvo. The cruse book and electrical book is around $ 40. and I think well worth it. Dana stopped making this unit in the early 90s and the only parts are hard to find. I also read that when the servo unit shorts out it takes the computer with it. When working the unit works pretty well but you have to get the spedo cable working smoothly and not jumping. The cable that goes to the throttle can be changed out to fit your car , May have to look at the pick and pull for the correct length. To me it was worth the effort to repair this system but the green books are needed . Not hard just a lot of parts to install.

Eck 242 81