[projectRDM]

There is no 'correct' way. You can cut back and insulate or completely remove from the ECU plug, it doesn't really matter as long as it's not going to ground out later. For the brown lead, it does indeed split up through out the harness, just cut the leg from the circuit not need, then insulate the OE splice. If that's not clean enough, cut the splice out, then reconnect with solder and heatshrink.