If it got worse changing the sensor you may have a bad one, it shouldn't have gotten worse. Wire corrosion can happen over time and these cars are old, regardless where the car has been. CRC makes a battery cleaner and also a protector, if you spray it on the grounds it will strip off any corrosion. Cheap enough to try. Also make sure the power junction box with the cover by the passenger strut tower is tight , these can cause funky things to happen when they loosen. Keep at it, you will get there. good luck.
