My truck is a 99 Bosch with 4.0 engine and SAI. I am running an ECU from a 2000 4.6. It runs fine, better than with the 4.0 ECU, but always throws code due to lack of additional coolant temp sensor in the bottom of the radiator. Additionally, one of the oxygen sensor connectors of the wiring harness is damaged by the previous owner. Also. my coolant temp gage works only occasionally. It seems to be a wiring issue between the sensor and the BeCM (I swapped BeCMs and measured resistance at the sensor). In my experience oxygen sensor circuits are often sensitive to resistance changes from factory values. Given all the issues above I am contemplating replacing the complete engine wiring harness instead of trying to troubleshoot and repair the old one. How big of a job is it? Can the wires be snaked through, or do I need to take things apart? I suspect that I may need to remove intake manifold. What else will need to be removed to install a new engine wiring harness?