1972 Ford Courier electrical problem

I have a 72 ford courier with an electrical problem. Any time I hit the brakes or use the turn signals, power drops to other electrical Components, then comes back (radio, head lights get flickery ). Also, the flasher or a relay located under the dashboard on the left hand side of steering wheel will all of a sudden start making a loud flickering sound. I replaced the voltage regulator to no avail. The carburetor and fuel pump are after market. Could they be drawing too much power? Where should I start? Thanks in advance.