Did a local JB4 harness upgrade this weekend and took a few photos in the process to make our DIY. It's a pretty easy process but you will need to follow the directions.
When you get the JB4 upgrade you'll get the new control box and a new power wire. Basically you'll be inserting the new power wire in the DB25 connector and relocating three wire pairs to new positions. What used to be IAT, RPM, and 5v are relocated to CAN+, CAN-, and chassis ground. Numbering is read from the female side of the connector only and the corresponding male pin will always go directly above the female pin. e.g. do not cross up the brown and white wire looms. It should look just like the photo below.
The most common mistake is mixing up the brown and white wires. All numbers are from the FEMALE side only. The male pin always goes directly ABOVE the corresponding female pin. Please study the photo of the gray subconnector below carefully. The photo leaves no room for confusion so any problems you email in regarding the gray subconnector will only be met with ridicule if you do not study the photo.
The last photo shows you where the new power wire goes in the car when installing the harness. More details directions for the power wire install here: http://www.n54tech.com/forums/showthread.php?t=10880
For Pin Out Customers:
Instead of relocating the three pairs within the PnP harness you will simply install those three wires in new locations. You should disconnect and reziptie the four new bundles together to avoid install confusion. You will also insert and install the power wire as shown below. This might also be a good time to upgrade to a full PNP harness
Large black subconnector:
yellow: slot 10 (boost, yellow wire)
black: slot 32 (ground, red/black wire)
purple: slot 7 (boost solenoid 1, white/gray wire)
green: slot 14 (boost solenoid 2, white wire)
gray: slot 9 (fuel pressure, yellow/red wire, connect on all models)
Red loom previously from large black connector: slot 17
Small black subconnector:
orange: slot 6 (oxygen sensor 1, yellow/white wire with 525 stamped on insulation)
blue: slot 7 (oxygen sensor 2, yellow/white wire)
dark red: slot 7 (throttle position, yellow/white wire. May be blue/white on 535)
White loom previously from large black subconnector: slot 14
Brown loom previously from large black subconnector: slot 1