big voltage drop

[V6cious]

been a while but I need help again guys I had a problem getting my alternater to charge but found out that it was the brown wire broken going to the volt light now it charges but slowly drains the battery brought a new battery last night and it ran great for 1 day the voltage reading after installing new battery was 14.3 and now after driving it is down to 12.9 to13.3 and if i lean into it it'll drop to 12.5 12.6 I had my alternater bumped up to a 120 amp already so I need to stop from blowing another headgasket

 

[onefastcar]

I would look at your ground i had same problem and it was loose, i actually added one to the frame and my voltage is at 14 something most always.