I have a 87 300D with the same tach and ABS problem. Tach stops working ABS light comes on, idle speed drops and it's rough to start. The manual says if the ABS light comes on, but the brakes work, it's the alternator not putting out the required voltage. A voltage check confirmed this. 14.2v when everything is jake and 13.5v to 13.7 when tach stops and ABS light is on? Any thoughts on the voltage regulator or alternator being the culprit?