Bought a used 88 MB 420 SEL. At that time the speedometer/tachometer was not working completely. No mileage count. Replaced by a MB mechanic with a ebay new OEM one and now have a new problem. The speedo will go up to 40 mph perfectly and if I go faster than that it swings wildly above to 120 mph even though I am only going 55-60. If I take my foot off the gas the needle returns to actual speed. I was told it might be sensors???
Can anyone advise me what I should ask for when I take it in. Don't want to be scammed since they don't seem to know what it is.
Thanks for your help.