84 Buick Skylark

Mornin all,
Very frustrated Buick owner here. I have a 1984 Buick skylark 6 cyl that is being very disagreeable with me. I have a bit of a multi faceted problem that I believe can be traced to one thing but not sure if I'm right or what to do about it. When I bought the car, I had to run a bypass to run the fan. The bypass is a kill switch split into the fan switch wiring running directly to the battery.
As for the actual problem, more noticable at night, I have a lot of noise through the radio system, dashboard light array dimming, headlight dimming, if I have to use the wipers, they move much slower than they're usual speed, etc. The dimming an radio noise becomes more pronounced when I use the breaks(vaccuum assist) and slow down let alone stop. Not sure what else I can post here, but hopefully someone may have an idea as to whats happening. If anything, both the alternator and the battery are new and according to tests at Advance auto, they both are pushing the correct amperage,etc.
Thanks for any help that can be given.
James