Big electrical loads, grounding kit?

[Blindedlegacy]

1986.5 na 5 speed. Had this problem since i had the car and just wondering if someone has or dealt with this similar issue. Every electrical load is "big". To attempt to explain, if i have my turn signal on the gauge is going from 14 to almost 12 with each flash. headlights, blower motor, window motor, and my dual e fans (would understand that one because they have some serious draw) i thought it was probably just the gauge wearing out on me but i hooked a meter to it and it showed the same thing. its my daily so i dont want to just start tearing into things if there is a simple solution. battery and alternator are about a year old. Also has anyone used the grounding kit and seen results? asking because i want to get a decent sound system in there and do not want it to kill the car lol