Q: Install front brake calipers on this car on 2001 Mercury Grand Marquis

I have replaced the front rotors 2 times and the calipers, and pads. At about 40mph, I am getting brake vibration like the rotors are bad. It is on both front wheels What could be causing this? What should I replace next?

Just inherited a 92 Prelude and the fuel gauge doesn't work, so have no idea how much gas is in my car which has me constantly filling up. I got the car about 2 months ago, before that it had been sitting in my son's garage for almost 3 years. The night I finally got to take it home, the gauge worked, but when the front brake pads caught fire (because the calipers locked up), and I had to park the car, the gauge went off never to turn on again (I do not know if these things are related). A friend of mine and I have tried to figure out what is happening, but its kinda weird because following the schematics for the gauge cluster, everything seems to points to the dimmer switch (which works). I don't know anything else to tell. Does anyone have any ideas?.....