I've almost wrapped up the installation of a used '04 motor in my '03 Disco. The 'new' engine is in, tranny is bolted up (by far, bolting and unbolting the transmission is the worst part of the swap), and I'm finishing up the wiring. I was able to uplug all parts of the harness and reuse it EXCEPT for a loom that runs down the top of the tranny and supplies the O2 sensors and other things. There are 10 wires in this loom, so I just cut it and resoldered the connections. However, there are two wires out of the ten that are the same color (white with blue trace). They are both for the rear O2 sensors (along with two other wires per sensor - both also have a red with black trace and then one sensor has a yellow wire and one has a green wire). My question is, should these wires be sensor specific? Since they're the same color, I'm hoping they're not. The RAVE electrical circuit diagram (pg 53) shows the O2 circuits, but doesn't really explain what each wire does. Since each sensor has one wire that is a different color than what the other sensor has, I'm hoping the common colors are the heating circuits.

Thoughts?

 

The different color wires are the signal wires from the O2 sensor to the ECU. The other wires shouldn't make any difference.

 

Great. That's what I was hoping.

 

That's really surprising that you had to modify the harness, I was able to use my old 2002 harness on the 04 motor with no changes other than swapping out the temp sensor in the intake manifold.

 

Were you able to pull the harness that runs on top of the tranny all the back to the t-case? That's the part I cut b/c it looked pretty tough to chase down and release all the plugs and harness attachment points. RAVE doesn't mention this part of the harness at all, so I'm wondering if it's only on 03/04 harnesses?? RAVE was so detailed with everything else, I was surprised this part wasn't included (I had to replace the coolant sensor plug too, btw - weird that an '03 is different than an '04).

 

I think the coolant sensor changed mid 2003 somewhere. I have a couple of unexplained differences on my 2003 wiring in the engine bay, some things are not in RAVE and things in RAVE that are not on my harness. I kept notes and pictures and tagged everything for reassembly, so hopefully it all works out. In your case it's a jigsaw puzzle.

 

NOh I see what the problem is, not that it matters now since you've already completed the swap, you followed rave and tried to remove the wiring harness. What I did was leave the original wiring harness in the engine bay and just disconnected the points where it connected to the engine sensors. I think its an easier way to go, removing the entire harness from the chassis as rave explained seemed like a nightmare.

 

Agreed, now that I've done it, I would leave the harness in next time simply b/c of the part I had to cut. However, pulling the harness through the firewall wasn't as big of a deal as I thought it would be.

 

Well the important thing is that you made it work, and learned how to go about it, and learned not to follow instructions next time . Rave is very good, but like most service manuals I've seen asks you to remove more than is necessary, and sometimes things that just don't make sense.

 

It's like the warning you get with your GPS: use your common sense when things don't look right.