Q: Sporadic issues with eletrical system of the car

I have issues with the radio, speakers, clock, odometer and speedometer in my car, sporadically going off and back on again. I took it to the dealership and they found speakers and radio not working, but I told them that they go off and on and that the issue happens occasionally. I eventually replaced the radio and speakers, which was very expensive. There are still intermittent issues with the speedometer,odometer and clock lights. The worst problem occurred recently. My lock seems not to function well. It sometimes doesn't work when I push it manually, as the remote is not working. I manage the door lock but the problem still happens from time to time. I would like to fix it but they haven't given my any solution at the dealership. Please give me some advice. Thank you.