2007 mercury 4 stroke. Why is it blowing 25 amp fuse?

SOURCE: 2001 Mercury Mountaineer keeps blowing the PCM power diode (fuse #19)

Check all of the battery terminals and cables and check the wires on the starter/selonoid, start from the battery and follow the cable out and check all conections , clean and tighten them and if it still does it the starter/selonoid is bad and needs replacement...

SOURCE: 2007 mercury montego rear light

  You need to be more specific about which rear light blows the fuse(interior,stop or tail). If the car has an aftermarket alarm or autostart I would look there first, they are usually installed poorly and create these types of problems. 

SOURCE: blows fuses

SOUNDS LIKE THE ALARM HORN IS SHORTED, CAUSING FUSE TO BLOW.
TRY UNPLUGGING ALARM HORN & SEE IF FUSE STILL BLOWS.
IF IT DOES NOT BLOW, REPLACE ALARM HORN.

SOURCE: My 1997 Ford F250 power stroke deisel 7.3 keeps

Fuse 17 10amp protects the following 1)transmission control switch and lamp. 2)brake fluid level switch 3)warning chime 4)diesel warning lamps display 5)fuel water switch 6) low vacuum warning switch 7)instrument cluster 8) switch lamps,,,,,,,,,,,,,, i think your problem on transmission control switch, check also brake light and brake switch

SOURCE: 2001 mercury grand marquis

Check under the dash at your Brake pedal interlock switch. It is timed with the gearshift Interlock and Ignition switch. This switch usually gets hit by feet and dislodged or broken. When you shift out of Park, the switch is toggling to a broken piece and shorting out.

The brake interlock switch is at the top half of the pedal lever. The other part of the Interlock uses a rod or cable in the steering column Ignition switch and mates with the shifting mechanism.