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1983 Mercury Cougar LS speedometer

Just this morning I was on my home from work, and my speedometer played around on me. It moved up and down from 5mph to 25mph about three times before it finally “died” and stayed at nill mph. The tachometer which keeps the milage also died and now I can not figure out what happened. Back in August I had a similiar problem however it made a alot of noise and it sounded like the cable broke. This time there was no noise. If you could help me come up with solutions or things to try before I take it back into my mechanic it would be helpful. I have had the speedometer repaired at a special shop in California through shipping and handling. It great once I had my mechanic install it and repair the cable. But now I dont know if it could be a fuse or something electrical. This car is supposed to be very electrical, and I have considered replacing the voltage regulator and the alternator. Could the regulator cause any of these problems? What can I do? I have checked the fuses, I have found one burned out, and have decided to just replace all of them fearing they could just be too old. What else can I try?

If the tachometer also fails to register along with the speedometer most likely the problem is with speedometer head. Especially if you heard a noise at an earlier time.

The tach and speedo are analog in this vehicle. Not electronic.