190d having odd problems with turn signals and pegging gas gauge
 

so about a week ago my 1986 300,000 mile benz 190d odometer stopped working, i just kinda brushed it off seeing that it has 300k on it and was going to take the dash apart the following weekend. well just today on the way to work the gas gauge started bouncing around whenever i hit the brake. i figured it has the same problem as the odometer has. then when i started putting my turn signals on my open door noise came on everytime my signal blinked. tonight i was driving around and someone said that my backup lights were coming on when i was making a left turn, now i have to say that i did replace on of the brake lights with an incorrect light bulb. so i was wondering, if that could be the problem. also my battery is almost 90k miles old and was made in 1999, well installed, im really freaking out right now becuase i dont want to get in an accidnt if something goes wrong.:confused::confused::confused::confused: