All your wiring,and many other things run through the bulkhead,in the engine compartment locate the wiring harness where it goes through bulkhead,peel back the rubber grommet push a stiff wire through(copper earth lead)with an eyelet formed on the end,and have someone locate it on the inside and pull it through with your wire tied/taped to the end(your end) it's fiddly but it is the way it's done.
Rich
October 2008