kaking

i have a 89 coupe that im in the middle of swapping and i want to make sure i have no more electrical problems...the previous owner raped the body harness. the planned is to just replace the front section fender to fender. picked up a clean one from a 89 hatch at pick n pull and now that im comparing the two they seem to be a lil different. the new one seems to have less wires that run under the passenger fender well.

so for those with experience replacing or repairing body harnesses...
1. how tedious is swapping a body harness?
2. can u replace portions instead of the whole thing? like is there plugs under the dash that you can undo in order to just swap the engine bay portion instead of the whole car?
3. if u can do #2 are the hatch and coupe compatible?...if so does it vary SOHC to DOHC?
4. painless wiring kit...has anyone done it???