Wiring harness swap tips

[jeff351]

Any tricks for removing/reinstalling a wiring harness? Prepping to do a 4.0 swap from a 94 XJ into my 89 MJ.

Guessing its just a matter of taking lots of pictures, labeling as I go, and referring to the service manual to ID what everything is?

 

 

 

[mjeff87]

The engine side harness completely separates (via multiple connectors) around the relay center area.  There are 2 sub-harnesses per se, one for the TCU and NSS (if auto equipped) that plugs into the "upper" main harness that runs from the CPU either directly through the firewall or via the C101 connector on older Renix models, and the headlight harness that plugs into the lower harness around the driver side headlight/front right radiator header area.  That part of the harness runs from the C100 connector (engine side of the fuse block on the firewall side, under the brake booster).  When I swapped an 89 4.0 harness into my 87 2.5 MJ, I disconnected the main harness and removed each corresponding section of MJ old harness and replaced it one by one with both sections of the new harness, then plugged it all back up together again.  You can label all of the connectors if you want to, but outside of the injector wires, each connector is pretty much unique and only fits the same other side connector, so it's pretty easy to figure out what plugs into what, and what sensor hooks up to what connector.  The harness pieces should be well molded/shaped to where the entire harness falls right back into place, making things pretty logical.  The only issue I had was the HVAC blower connector on my "new" harness was a different design than my old one.  I just swapped in the new blower motor that had the newer style connector on it and plugged it up.

 

All that said, I did have the liberty of swapping harnesses while I had the entire drivetrain out for a swap, which did make it much easier....I did label all of the connectors as a precaution, but I really didn't need to.  Good luck 

 

edit:  there's a tiny captive bolt in the center of the C100 connector on the engine side that you have to unscrew (it's captive, so it won't come the whole way out).  It's kind of a PITA to get a socket on, use a 1/4" drive with a universal or a swivel socket and a short extension to get on it.  IIRC is a 6.5mm bolt head.  You won't be able to separate that bulk connector the whole way without unscrewing that (very cleverly hidden) bolt.

[Limeyjeeper]

Label EVERYTHING and be prepared for the wiring schematics to sometimes have the wrong color documented for a particular wire. Photos are ok but without a high definition camera it is tricky sometimes to see what color is on what pin. I like to document big plugs like the cab to dash harness. It will save confusion later.

[pizzaman09]

Not in Comanche but on another car I have I did a very custom engine head setup.  I made a handy notebook were I labeled every wire and hose I disconnected on both ends with a number and made a corresponding entry as to what they were in the notebook.  This also was done for bolts and hardware where I put them in numbered zip lock bags with a description written on them.  That high level of organization made my life much easier when I installed the unique custom engine head a year later.