When wiring up the O2 sensor, reroute the 12V supply to the 02 sensor heater through a separate inline fuse. My o2 sensor went short circuit once, and blew another fuse down the line, that was impossible to trace.
I fixed it on the side of the road by blowing the fuse twice, and cutting the heater 12V wires to keep it going. I ran without an 02 heater for the next 3 years.

I spent a lot of hours debugging damn strange problems with my CA18 back when we did the transplant back in 1994