What connection do I need in order to use 4 TENS pads?

As for hooking up 4 TENS pads, there are some caveats to cover first.

1. The use of the Boost and one pair of TENS pads will be 4 times more powerful than the use of two pairs of TENS pads. However, the use of two pairs of TENS will allow you to spread out the coverage of a contact treatment.

2. While you can use the following information to use two pairs of TENS pads, it should be done from a single generator which shares a common ground. Do not attempt to do this with more than one generator, as electricity will always take the shortest path, even if that means both generators flow into a single generator's ground.

To use two pairs of TENS pads requires two TENS cables. A Spooky2 kit only provides one TENS cable.

Connect one TENS cable directly to Out 1, and the other directly to Out 2.

Remove the boost to make sure you are only wiring up to Out 1 and Out 2 if you prefer to keep things simple. Otherwise you will wire one pair of TENS to each Output. If you leave the boost on, ensure that you are wiring up to Out 1 and Out 2, not a boosted port.

Within the program you are running, change the program to use Follow Out 1 vs. Inverse+sync. so Out2 outputs the same as Out1. Be aware that the graphic for the boost won't show any output because if you use these setting with the boost device, the outputs will cancel each other. Failure to use Follow Out 1 will cause the two TENS pairs to interact and cancel out.

For more details, please check the link:
https://www.facebook.com/groups/spooky2/permalink/682112968617276/