How To: Make Your Own o2 Extension Harness

[hEaT]

Like many others who have done the SVT header swap, I noticed the wiring for the first and second o2 sensors would not easily reach the new sensor locations. The wiring loom could be undone to let the first sensor reach, but not the second for me.

You can see from the top here, the two blue connectors are too far apart and the ECU side cannot be undone anymore:



Here's the cheap way to do it which requires no modification of the ECU or o2 side of the harness and is easily installed/removed. Plus, it's more fun to make your own stuff anyway.

Supplies Needed

• Wire Cutters (Dykes)
• Wire Strippers
• Crimping Tool
• Electrical Tape
• Heat Shrink and Heat Gun (Optional)
• Butt Connectors or Similar Connector
• o2 Harness From a Junkyard Car

Here are the connectors I used. You'll be using the 18-22 gauge connectors. The wires vary in size, but not enough to need a different size. These are cheap, but you need to provide insulation since they are just bare metal:



Here is the most important part, a donor o2 harness. I got mine for $10 from a local yard. It came from a late-90's Escort. Any harness should work as long as it uses the same 4-wire plug. You need to cut just above the o2 sensor and then past the connector on the ECU side of the wiring to give you a piece like so. The left side is the o2 side and the right is the computer side.



First step is to unplug the harness and remove the unnecessary crap attached to it:





Here is the donor ECU side of the harness plugged into the o2 sensor:



Here is the old o2 sensor side plugged into the ECU side on the car:



To get this all to work, you are just reversing how the connector works by connecting all the wires to make a patch cable.

First step is to the cut the wires to the length extension you need and strip all the ends:



It's EXTREMELY important that you make sure you are connecting the correct wires together. Looking at the connector plugged together you can see the position of the wires and how they pair together through the connector.

It's always a good idea to check continuity on the wires you'll be connecting to make sure you have the right ones and to label them:



Nothing sucks more than getting your connections together and realizing you crimped the wrong ones. In this case, one of the white wires went to purple, the other to the white/red stripe, black to grey, and grey to green/black stripe.



Next step is to use you preferred connection method and connect the wires. I used the butt-connectors and then heat shrink tubing over them. I then heat shrinked the whole harness to give it a cleaner look. I used electrical tape over the individual connections to make sure no water could short them. While unnecessary, this is something you don't want shorting out so I wanted to make sure. It takes away from the aesthetics unfortunately, but function over form in this case.

Here is my finished connector:



It now can do this:



Check continuity again through the pins to make sure all is well:



Here is the patch cable plugged into the ECU side of the car's connector:



Here is the patch cable hanging down, now easily able to reach the o2 sensor:



Now just secure the connector to keep it from hitting the header or getting snagged on anything:





Done! The only cost is how easily you can get the donor harness and a little bit of time.

[evanjfrancis]

wow. not bad =)

[recar]

Is the connection water proof?

[hEaT]

Originally Posted by recar

Is the connection water proof?

I don't see why it shouldn't be. Each connector is heat shrunk, individually taped and then all three taped together.

You could easily use waterproof butt-connectors, but I think they look like crap and would ruin the more "OEM" look I was going for. One less thing to question at emissions.

[G-forces]

Nice work hEaT... this should be considered for a sticky!

I really like using slight wire twist with the folding brass crimps (the kind Ford supplies with the upgraded TPS pigtail kit) and high-silver solder. Very strong when done. Just another choice for your already thorough thread.

[Stolle]

anyone know where you can get the pigtails needed to make one of these brand new?