Let me clear up a little confusion here regarding the jumper blocks.
The gen 3 uses the same jumper blocks PRO has been using for years. They are exactly the same as the ones found on the Gen 2 system.
The gen 4 battery rack uses a proprietary jumper block design to only be used on the gen 4. There are 6 ITT gold plugs on the bottom row of a gen 3 jumper block and 6 corresponding female ITT's on the gen 3 battery rack, this allows us to wire all 3 batteries independent of each other. The gen 4 jumper block has 4 ITT gold plugs on the bottom row with 4 corresponding female ITT's on the battery rack. Although it is possible to put a gen 3 jumper block on a gen 4, 2 of the 6 plugs will not be connected to the battery rack due to their female counterparts not existing and thus it will not function as designed. There is also a wiring difference as to which battery is doing what between the gen 3 and gen 4. We do not recommend trying to use anything that it wasn't specifically designed for. We do not wire custom jumper blocks for either the gen 3 or gen 4 battery racks. We offer 3 for the gen 3 and 1 for the gen 4.
I hope this helps.
GPI PRO Systems