I have a 97 M900 and the speedo/tach went south and were fugly to boot. Changed out to a digital Acewell speedo/tach combo. I think it was around $100. Bought the Haynes manual ~ $25 and it includes a wiring diagram that I blew up and laminated.
If you can read and breathe, you can change it out, I did and am no mechanic by any means.