Whats up guys. Im in need of some advice please. Electrical issues.

How is it going?
I have a 1966 Mustang and its been running fine until today?
Its electrical issues. I've replaced the starter solenoid, alternator, and voltage regulator. I had the same issue about a year ago but I just had to get the voltage regulator replaced and I also replaced the starter. Now when I get it jump started the voltage drops on the battery and the alternator doesn't charge still. I also just got a tune up around 3 weeks ago. The only thing I can think of now is some type of wiring issue. I be grateful if anyone could help me out.
Thanks.