Really need help Major Issues!!

i have 91 civic hatch and when i push the brake my headlights, dash lights, dome light all dim when i push my brake and sometimes my alpine head unit will shut off and come back on when i push the brake also another problem i get in the car to start it and i turn the key and the car won't even try to start. the main relay clicks like it is supposed all my lights, dash lights and radio work but the motor won't even crank! it don't do this all the time but more and more often now.it is a 1.5 manual 4spd if that helps thank you to anyone who can help me