So I did you fix the antenna issue? I just installed an aftermarket stereo and I'm having the same antenna poor reception. I don't have a tester, as I'm not an electrician, to check if it is also getting 6V rather than 12V. Can it be connected connected together with the red wire instead to get 12V?

I'm having same problem, can't find a solution online, gonna try unplugging antenna or fuse while it's up with factory radio then hook aftermarket one up. At least til I find a proper fix

same issue ! so what to do? to change radio ?

I have the same problem