P0743 code but transmission convertor locks up

You'd have to look at the wiring for the 2 plugs that power the gauge cluster. The PCM is capable of supplying ground (as it does on several circuits), but it's also possible that the cluster grounds to the firewall or the dash sub-skeleton. Section 8W of the FSM will have all the wiring diagrams.

I happened to have the '02 FSM already open ("I'll take 'How to know if you're a regular on Wrangler TJ forum' for $500). Looks like the ground is on circuit Z2, which I'm 90% certain is going to be a body ground as opposed to a PCM-supplied ground. I'm also guessing from this that the CEL is lit up via logic on the cluster circuit board + pin 12 which is the PCI bus.