2ZR-FE Engine Wiring Harnesses Disection

Toyota Engine Harness

The inner workings of wiring harnesses can be a tangled mystery, and most people in their right mind wouldn't cut one up. Even with all of my dealership and aftermarket electrical experience, I have only opened harnesses a couple times. When it comes to diagnosis, the only information the manufacturer gives you is: diagrams, connector pin-outs, ECM input/output, and voltage/resistance checks. This information is useful and does get you an answer, but now you will be able to see what exactly is happening inside the loom. 

Delphi HES Circular Connectors

First, I'll tell you why I'm doing this. Since the 2zrVios is now for race use only, I purchased a set of Delphi HES Circular Connectors to create a single wiring connection to the car. Now of course there will still be the large power cables to the alternator and  starter I'll need a junction for but I'm mainly referring to the engine sensors and transmission speed sensor. So lets get started. I like to categorize the harness into 4 parts; 1-Engine sensors, 2-Power supply, 3-Grounds, 4-Main fuse box pass-through. Here is what this harness looks like spread out:

Engine Sensors

Sensor Plugs Separated From Grounds and Pass-Through wires

Shielding Grounds

Shielded Crankshaft Sensor Wires

There are many different sensors on engines today, and all of them have a important role in maintaining harmony.  Some priority sensors even have a grounded shielding around their signal wires to protect against EMI. Here I will list all of the sensors and where their wires go:

Crankshaft | *1/*2-ECM * Ground shielding
Camshaft | 1/2/3-ECM
Knock | *1/*2-ECM * Ground shielding 
Cam Advance OCV | 1/2-ECM
Coolant Temp | 1/2-ECM
A/F Ratio AND Rear O2 | 1-12v supply/2-ground/*3/*4-ECM * Ground shielding 
Injectors | 1-12v power supply/2-ECM
Coils | 1-12v power supply/2-ground/3/4-ECM
Evap Purge | 1-12v power supply/2-ECM
Electronic Throttle | *1/*2/3/4/5/6-ECM * Ground shielding
​Voltage Regulator |  1-12v(BATT)/2-12v(IG)/3-A/C AMP/4-Meter
Oil Pressure | 1-Meter

Power Supply

Power Supply Elements

Engines need voltage to run, the same 12 volts you charge your phone with is powering the engine sensors as well. All of the sensors get their power from the engine fuse box, witch is powered directly from the battery. Now of course the power supply system has many fuses in place for redundant safety and circuit protection. So lets look at what individual circuits there are for the engine harness:

Coils/Injectors | AM2 15A
A/F (sensor1)/Rear O2(sensor2)/Purge | EFI 20A
​MAF | EFI2 10A
Voltage Regulator | Batt- ALT-S 7.5A/IG-GAUGE 10A

Grounds

Ground System

This is pretty self explanatory. For any solenoid, switch, or sensor to operate properly we need to have a clean ground signal. The entire collection of grounds terminate here at the valve cover, here is all of the ground wires in the harness:

ECM (C19) #2/#4
Coils (C11/12/13/14)
Crankshaft ground shielding 
Knock sensor ground shielding
A/F ratio ground shielding 
Electronic throttle ground shielding 

Main Fuse Box Pass-Through

Pass-Through Wires

Ok guys this is the last part, here are the remaining wires passing through the fuse box. Whenever the ECM, Generator, Meter, EVAP system, or ABS systems need to communicate, these are the wires performing those duties:

Rear O2 Sensor
Generator signal to meter
Oil pressure signal to meter
EVAP Canister Pump Module control
Starter Signal
Reverse lights signal
Clutch switch signal
Cruise control switch signal

I believe thats all there is. I hope this explanation helps to show that engine harnesses are just a bunch of wires and not really that complicated. These harnesses are mass-produced to be reliable and easy to check for faults, so the only tool you will ever need to inspect them is a DMM. When it comes to repair that's up to you, some prefer crimping while others suggest soldering. You can also go check Ebay or the salvage yard for a whole replacement. I personally like to have a couple spare harnesses for the extra plugs, and when I need to repair a wire I prefer soldering and a sealing type heat-shrink. Feel free to provide some feedback or ask any questions you may have, and good luck!
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