Those two pickups sound very similar to me, in both tone and output. I think you might be hearing the differences between two guitars, and/or the 500T is simply adjusted to be louder.
As suggested already, check to make sure the vol pot in the "V" with the JB is 500k, raise the JB, lower the 500T, and if that doesn't help enough put either a ceramic or an A8 in the JB.
