Battery Voltage Sensing Fuse Blowing Often

I have a 99 Mercury Vougar V6. I changed the alternator recently because it was cracked. (This was my fourth alternator). Within hours of replacing it my battery light went on. I immediately brought it back to the mechanic and found out that since I bought the alternator separately from the person who installed it he could not guarantee the labor.

He diagnosed a blown Battery Voltage Sensing fuse and replaced it. Since then I have had to change it 6 or 7 times.

When the alternator was installed I noticed that I had trouble shifting smoothly. The RPMs would drop quickly from 3000 to 1000 and then back up to 1500. The fuses blew most often under medium to hard acceleration or around a corner but sometimes for no reason at all.

When I drove below 2000 RPM I did not blow many fuses, had smoother shifts (and had really great gas mileage). I never had problems on the highway even when running for long periods at 3000 RPM.

I decided to return the alternator, bite the bullet and pay to have a new alternator installed from the mechanic. I now still have the problem with the RPM dropping and am worried this is all going to start all over.

Is there any relation between the alternator/regulator and the RPM? Or is there a break-in period on alternators that cause rough shifting? If I start burning fuses do you think I will have recourse with my mechanic to look for a short if he caused one while installing the first alternator?

I guess this is all hypothetical for now but I appreciate the help.

Never heard of a alternator break-in period.Are you buying your own parts then taking them to a mechanic for installation? Maybe its just me but I would never do this as a customer or use customer supplied parts if I was the mechanic.

How did the alternator crack (some kind of prying on it)?

This is a time I would like a theory of operation explaination and a schematic to see what this fuse is protecting and its location in the circuit.

I don’t know about your case, but some cars will increase idle speed if the battery voltage goes too low. This is to help recharge the battery.

Hopefully replacing the alternator stopped the fuse from blowing anymore. Check the voltage between the alternator ouput lead the positive battery post while the blower and lights are on. If the connection is good there should be very little voltage between the two points. Voltage across the battery should be around 13.5-14.8 volts while the engine is running at around 2500 RPM.