Question/help with 996.1 engine harness change
 

I have a 2001 Carrera cab. it's throwing a P1229 which is a short to ground on the #3 injector circuit. The engine seems to run ok, it's a bit rough when cold and at idle. The previous owner has hacked the wiring harness; as far as I can tell the #3 injector wires now come directly from the #5 injector. The wires are spliced in a few inches from the #5 then run across the top of the engine and directly to the #3. There is no sign of the original wires from the harness near the #3 injector.
How does that even work?
The wiring diagram shows that the injectors share a common ground but the other wire connects to a separate valve!
I can't see any breaks in the insulation but have not yet put a meter on them.

I picked up an engine harness on eBay and was planning to install it to resolve the issue but I can't seem to get access to all the connections even after dropping the engine the prescribed 4cm as described in the injector change procedure. Is a wiring harness change possible with the engine still installed?

Any help or suggestions would be greatly appreciated.