Approx. 1 volt drop between battery and fuse box
I haven't had an old Mopar yet that didn't have a voltage drop between the battery and fusebox. Nothing to really worry about. If wires start to smoke, that's when I would worry.
If you want to be proactive before having an issue, follow the instructions and diagram the Professor up there ripped off from Mad Electrical for his lecture.
I like Tony. He's helped me out more than once