We can put an end to the speculation easily.
OP, assuming that you are running this amplifier in bridged mode please perform the following tasks.
1. Purchase a banana jack.
**Prior to the next step remove the NL4 from one end of a speaker cable. This cable will run to the first sub closest to the amplifier.
2. Attach the banana jack to the end of the speaker speaker cable where the NL4 used to be. The jack will have a hump on one side, this is considered and marked as the negative side on most banana jacks.
**When performing the following step you will use a DVM or continuity tester to confirm that you are attaching the correct wire to the correct connection on the banana jack.
3. Attach the wire running to the NL4 -1 connection to the negative side of the banana jack.
4. Attach the wire running to the NL4 +1 connection to the positive side of the banana jack.
5. DO NOT attach any other wires leading to the NL4 to the banana jack. If additional wires exist fold them back and insulate them from the banana jack and from each other.
6. set the 3602 to bridged mode using the switch on the back. (refer to photo)
7. Turn the channel #2 sensetivity knob on the front of the amplifier to OFF. (full clockwise)
8. Plug the banana jack into the two (2) RED binding posts located on the back of the 3602. Note that the posts are clearly marked + and -. Be sure that the negative side of the banana jack is plugged into the post marked negative. (refer to photo)
9. Run a standard NL4 to NL4 speaker cable to the second speaker from the first speaker. A pair of 8 ohm speakers run in series will now have an impedence of 4 ohms.
10. Any combination of cabinets that lowers the impedence below 4 ohms must be run using a stereo configuration as the amplifier is not rated for 2 ohm operation in bridged mode. (refer to photo)
If all else fails RTFM or call QSC. Good luck, and I hope this helps.