I have had the alternator checked twice on my 85 Euro 190E 2.3 16V - they say it's ok. I have tested the voltage at the battery when the car is at idle - 12.5 volts. When I drive the car, the voltage stays at 12.5 for a while, then intermittently drops to 10V, then returns to 12.5V. (I recently bought a LCD voltage meter that plugs into the cig lighter so that I could see the erratic voltage when I drive the car.)
Is my alternator bad or do I need a voltage regualtor (I suspect a bad regulator would show over 14.5V being produced. Could it be a loose connection? Any advice would be greatly appreciated.