I found the online manual at gizzmousa.com
http://gizzmousa.com/file-copi...l.pdf
From the looks of it, you need to power the launch control using the black/white power source (assuming the RBs use the same wiring coordination I've seen in pretty much all the 4 cylinder Nissans I've worked on) It's the power signal that comes from the ECCS relay. On the KA/SR ECUs, it would be easy to accidentally use the backup power wire (Red) that is always hot. But all of those are powered by the brown ENG CONT fuse, not the green IGN fuse.
Now, the part of the unit that intercepts the coil signals is on a direct line with the coil pack main power supply (Blue/Red), which you should have tapped straight off the Black/Red which travels back to the IGN fuse.
A quick what's what on our coils is that they use the jumping energy principle of two closely wound coils. Basically, you charge a primary coil and there's a secondary coil wound in parallel to the primary. The primary is charged at all times, but when you cut the ground suddenly, the charge jumps to the secondary coil and the secondary coil is connected to the spark plug. The jump also causes a huge jump in voltage.
Anyways, the power routing should look like this:battery -> 30a fuse -> ign switch -> coil -> gizzmo -> ECU. Normally, the ECU is protected by the ignitor chip. The ignitor chip, from what I gather, is basically a resistor to prevent the ECU from getting accidentally fried by the possibility of the coils arcing funny. Nissan later designed the ECUs with an internal ignitor (S15 SRs are known to be like this). The Gizzmo unit seems to be designed to be on the low power side of the coil signal wire as the manual says it's supposed to work on an external ignitor chip system and to be placed between the ignitor and the ECU.
Normally when I see these fuses popping, there's something arcing high voltage back onto the either voltage supply or signal wires for the coil packs. The most recent one was some exposed wires at coil 1 on an SR were touching. One was the ground on the head that is connected to the secondary coil while the other was the 12v supply to the coil. The 40,000+ volts from the secondary coil were backfeeding the supply wire and popping the fuse. Given that you had to muck with a supply wire and all the signal wires, which are directly connected to the 12v supply wires, you may want to isolate your search to the launch unit's wiring and see if there's something arcing funny down there. You mentioned that the IGN relay was acting like it was stuck open, it would only take a 12v constant to make that happen. Also, that would trick the ECU to staying on, which would keep the power going to the launch unit just perpetuating the situation.
That's all theoretical, though. Since I really don't have any experience with the gizzmo unit