Welcome to NICO!
There is a picture in the FSM
http://www.nicoclub.com/FSM/Q45/
which you will be well served to read before you undertake this job.
There are also some pictures in a thread in IOM.
The sub harness is always replaced. Presume they failed the Ohm resistance test?
They can be reached by removing the alternator. But it is a good idea to remove the plenum and clean it, the lower runners, TB, IAC and EGR valves, and especially the EGR tube within as I guarantee it is crudded up if you have 80K or more since this procedure has been performed.
Necessary parts and gaskets are an additional 10% off this month at
http://www.infinitipartsusa.com
Call them and tell them you are a NICO member and want to take part in the sale.
Modified by maxnix at 10:05 AM 11/22/2008