Removing OEM Harness

I have a 2002 Lexus IS300 with a 2JZ-GTE swap done by a previous owner. The car was originally running on an F-Con V Pro piggyback controller. I am removing the F-Con V Pro and replacing it with an AMP EFI MS3 Pro. I have successfully removed the F-Con V Pro controller and the piggyback harness.

I'm now considering removing as much as possible of the OEM harness. My question is, how do I go about doing that?

Once possible method might be to identify each wire that was connected to the factory ECU and determine where it goes and remove it. That seems not very easy to do though. I would almost imagine that would involve pulling the entire OEM harness out of the car and removing wires from it on the bench. That does not sound like much fun.

Any suggestions about how I would attack this?

Hi Don,

It is usually quicker, easier and cheaper to make a new harness than trying to remodel and existing OEM harness. OEM harnesses are designed for convenience of installation on a assembly line, not for working on.

@BlackRex

I think that you are saying just pull the whole thing out and build a new harness. Fair enough.

Would there be any connections from the body computer to anything under the hood that I'd need to address?

Hi Don,

Most likely, I haven't done any work on those vehicles so I couldn't tell you for sure. The other issue to remember is that the current loom is at least 22 years old and has been exposed to heat, vibration and contaminants, and most of the connectors will be brittle and likely to break when being removed. You could potentially save and reuse some of the connectors, but it is a risk. The problem is always sourcing the replacements.

+1 vote for new harness due to age. Through no fault of your own you could do everything right, but put the harness back in the car after working on it and have all sorts of new issues simply because it's so old and brittle.

I've done a few IS300/Altezza's now and they are actually not bad to pull the engine harness. It pretty much all runs to the ECU box in the corner of the engine bay, there's 3-4 connectors that join the engine into the chassis which Toyota calls Junction connectors. So like starter, coil and injector power, VSS sensor etc are all junctioned in that box.

The catch with the IS platform is the BEAN network, also called MPX. its a single wire communication protocol and is difficult to interface with. Link makes a PNP that replaces the factory ECU that has an onboard converter, or there's companies like All4Swap that make interface boxes. Since you're planning around an MS3 you may need to modify the ECU box to fit the ecu and a converter, its a tight fit usually.

I would also suggest a new harness build as many are pretty brittle and crumbling apart after 20 years of heat cycling. I offer a complete kit of connectors, terminals and seals for JZ's on my website.