General:
Unfortunately the rubber used for sealing the contacts to the harness is prone to crack after years of use (pic 1) in the hot environment of the Z-engine bay. When it cracks, the moisture from the air can enter the contact and cause it to corrode. Of course the best thing is to replace the old shitty harness altogether but it's not the cheapest.
Contact cleaning:
Use a contact cleaner for the job. Cotton pads and a small gentle file
or a small screwdriver can come in handy as well.
The old contacts are usually brittle so be careful disconnecting them!
Use a smal screwdriver to pry away the wire/spring that locks them in place.
Clean the contacts thoroughly. Be careful with the file if the contact
is in good shape, you don't want to destroy the plating if it's still there.
Bend the contact plates (pic 2) with the screwdriver so that the hole
where the pin will be inserted gets narrower.
Fill the contact with grease. Use a high temp resistant (~200C or 390F)
dielectric grease. This will prevent future corrosion.
I used Electrolube SGB, contact treatment grease (see pic 3, click
on the pic to see a close up on the label)
Use some insulation tape to wrap it around the cracked rubber as well.
Harness repair:
If the contacts are in a really bad shape or the plastic is broken
then you can order new ones with a bit of harness
attached to them.
The ones that I know of that can be ordered are:
Injector connectors and alike: PN 24079-25P26 (~$20), they will fit
except for a plastic track on the injector connector that you have to cut
away. They come in 3 per set, see pic 4.
Coil connectors: PN 24079-85M00 - They come from a Pulsar and come
in 4 per set (~$50).
Since the new connectors come with a bit of the harness, cut the old
ones away. Expose the harness and solder (or crimp)
and insulate. Now, crimping is the best way if done right but I've
found soldering to work just as well. It is easier and gives
smaller connections.
WARNING! Note exactly how the old harness was connected so you can
connect the new contact likewise.
Remember to apply the contact grease, just in case.
You can also get new connectors that you crimp yourself on the harness.
I found it a bit tricky to do right though. Ask your Nissan dealer for
them if you want to give it a try.
Harness replacement:
The harness that most likely needs to be replaced is the EGI-harness
(called EFI in the service manual !). It is the harness between
the ECU and the engine. Do not confuse it with the Engine Room Harness
which is not the same.
This requires the engine to be taken out (pic 5). So if you have your
engine out for some reason and the harness is in a bad shape,
this is the time to do it (remember to replace the detonation sensor
with its harness as well).
Since the engine is out anyway, there's not much left to unhook so
just remove the brackets holding the harness as well as the ECU.
The hole through the fire wall is very tight, especially for the ECU
connector. Remove the plastic cover from the connector
and try to pull it through at different angles (turn it around).
I modified the new harness at the same time and let the AVC-R wires
run along with it..
I applied contact grease to all of the contacts to prevent corrosion.
The part numbers for the EGI harness can be found HERE on page 4-G-1 (Harness Assy EGI) for cars made until July 1990, on page 4-H-2 for cars made until September 93 and on page 4-N-3 for others.
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