Only a few need to be branched. 5VDC sensor power and sensor return (isolated from engine ground-go all the way back to ECU)(cam, crank, map, tps, oil psi, fuel psi). I also setup the injectors to have separate 12VDC Power per bank. To splice I strip and twist 4 wires into one side of an uninsulated but splice and crimp (same thing on other side of butt splice) then I solder. I insulated with heavy duty heat shrink with the heat activated glue inside to protect it from moisture ingress.
There are no splices anywhere else. I procured new connectors and pins for all sensors. Except the connectors that came from the factory harness, which were all “home runs” anyway.
All grounds are run to one point on the engine and I have the heads tied together with a ground strap. I’ll also add one from the block to the head.
EFI can be finicky with RFI. I always say if you think you have enough grounds, add more.
