I don't have the LBZ wiring diagrams, but if it is similar to the LLY, then this might help. (The PDF is for a 2005 LLY...)
The following fuses are all after the IGN A fuse, so try pulling them out one at a time and seeing if it stops blowing the IGN A. That might help narrow it down to a specific system.
IGN 0 (10A)
TBC (10A)
BRAKE (10A)
4WD (15A)
CRUISE (10A)
HTR/AC (30A)
HVAC 1 (10A)
IGN 3 (10A)
CRANK (10A)
If none of those fix it, it appears the starter relay is directly connected to the IGN A fuse, and that might be rubbing somewhere.
Since you are getting a 4x4 message, I'd start looking in that area. Good luck, and hopefully you don't have to buy too many of those stupid square fuses, they add up quick!