Electrical problems

I have a '95 plymouth voyager with 186000 miles on a 3.0 litre engine. The problem is the headlamps, hazards and brake lights are not working. When the button for the headlamps is turned on the brake switch buzzes and continues to buzz until the brake is depressed. The fuses all appear to be fine. I replaced the brake switch and brake lights worked on the first test, but upon testing again just a couple hours later they did not work. I just spent 500.00 for a new waterpump and timing belt. I hate to think it was a waste. I was hoping to get 200000 miles. It runs really well, but it is useless in this condition.