battery getting drained while driving

RE--read your first post. This really does not make sense. I'd see if you can "rig" a voltmeter from the battery up to the front and monitor it for awhile as you drive. You don't need very large wire as a voltmeter draws a tiny bit of current.

Almost any wire you have lying around will work.......no18 or larger. I WOULD fuse it, any fuse you have lying around 1, 2, 5A fuse in case you 'zap' the wire.

Did you make your own cable ends or have them made? Maybe the cable ends are not making good connection?

Monitor battery voltage while cranking, and re-measure "up front" at the starter to read the difference.

Do the same thing with your charging wire............check charging voltage at the battery and at the alternator stud.

What else is in the circuit............solenoids, disconnects, etc?