Originally Posted by Diseasel300

You need a Tach gauge from a 603 powered W126. Since that seems to have been a US-only thing, you're probably going to have to source a tach gauge from a US market car, 1986-87 300SDL or 1990-91 350SD/SDL. The OM603 was really only used in the W124 in Euro markets and the tach heads are physically different. The quickest way to tell if you have a tach from a gas car is to look for the red area in the rev range. Gas cars have it, diesels don't.


You have a car that's been hacked together with who knows what parts by someone with an unknown level of skill. You're going to have to resolve yourself to the fact that the factory wiring diagrams and traditional knowledge on these cars isn't going to apply much to yours. There's going to be a considerable amount of things you will have to track down and diagnose on your own or find a mechanic that can do it for you unfortunately.