DIY: How to tap ECU wires, and/or Junction Box wires.

[bananas]

Certain electrical mods such as Water/Meth injection, or Electronic Boost Controllers require that you run wires from your device to wires in the ECU box, or to the junction box (in the driver side footwell). If the wires are removed from the harness before tapping, you are much less likely to damage the thin (often 22awg) wiring. It's not immediately obvious how one can remove wires from the harnesses. This HOWTO demonstrates removal of both ECU box wires, and Junction Box wires.

Tools Required:
- Adequate Lighting
- Utility Knife
- Small Needlenose Pliers (optional)
- Longish Flathead Screwdriver
- Very small Flathead Screwdriver
- Wire strippers
- Electrical Tape
- Solder
Not pictured:
- Soldering iron
- Side cutters pliers






Part One: Removal of an ECU Wire

Follow the A4Mods.com ECU Removal HOWTO

The ECU has two individual connectors: one large and one smaller. I will demonstrate on the smaller connector.

The bare wiring of the ECU harness is protected by a black plastic shield that must be removed. The plastic shield is secured by a black zip tie and clips on either side of the shield. Using the side cutters pliers, clip the zip tie and throw it away. Use a needle nose pliers near the base of the shield/bundle of wires where the clips are. Gently squeeze both sides of the shield and it will pop off.



Locate the purple retaining clip and pull it out. You may need a small flathead screwdriver to get it started.



You will find that the harness is actually made up of smaller harnesses. We're most likely interested in the 2 small white wiring harnesses. With the purple retaining clip removed, these will pull straight out with no resistance.



Each wire is numbered, and the next step is to identify the correct wire. The wiring harness itself has certain wire numbers stamped into the plastic.... but it is nearly impossible to read. It's much easier to read the numbers stamped inside the ECU box.



We are now ready to remove an individual pin/wire. In order to do this, we need a very small screwdriver, or pointed razor blade (Xacto knife). Very carefully insert the screwdriver in the slot (located away from the bare wire). This will depress a retaining tab on the pin and allow you to pull the wire from the harness. There should be little to no resistance.






Part Two: Removal of a Junction Box Wire

The Junction Box is a set of wiring harnesses meant to connect ancillary components to the main ECU wiring harness, or other controllers such as the TCU or ABS module. On a B6 the Junction box located in the driver's side footwell. To access the box, you must remove two pieces of trim.
TODO: Post pictures of the two pieces of trim

The junction box is seen here.



After identifying the connector you are going to be working with (see the Bentley Wiring Diagrams), use a long flathead to disconnect the clips on either side (top and bottom) of the connector. This can be tricky because you have to do one side at a time, and they may clip themselves back in. After unclipping the first side, pull on the wiring harness and continue pulling on it until you have the other side unclipped as well. It requires some force to disconnect the harness, but do not use too much force. If it feels like you may be breaking it, you probably are! If you are having troubles, study how the clips work by viewing two pictures here and here.



Now we must move the retaining clip, like we did with the purple retaining clip on the ECU harness. The junction connectors' retaining clips are not as easy to work with, however. On the back of the clip, you will see two plastic pieces. On the other side, you will see a large plastic piece. These are all part of the same retaining clip. Push from the back, or pull from the front to move the retaining clip out. I used my needle nose pliers.

Push the two plastic pieces in:


Or pry the plastic piece out at this location:


As you pull the retaining clip out, you will feel two distinct clicks. The retaining clip has 3 possible positions: 0, 1, and 2. Position 0 is as you found it, fully inserted. Position 2 is out 2 "clicks", as far out as it will go. For the small pins, we want position 1, partially removed.

Position 2:


Position 1 (To remove small pins, the clip should be in this position):


Once we have the retaining clip in position 1, we will locate and remove the pin/wire. Each wire is numbered in the wiring harness:


The pins have retaining tabs which operate on the same principal as the ECU pins, only the orientation is different. The retaining tab on the wire is oriented down towards the center of the connector. Use your small flathead screwdriver and carefully push it up towards the pin, then pull the wire out.

Retaining pins in the harness:


Retaining pin from side, when wire is removed:







Part Three: Tapping the Wire

I'm no expert so I won't go into details about tapping, but to make a permanent connection you want to solder the wires together, then insulate the connection. Here is how I generally do it, but it's probably the wrong way:

Using wire strippers, score the wire insulation. It's very important to use the correct size wire strippers. Mine are labelled by AWG.



Using the utility knife, CAREFULLY make a cut along the insulation. If you are not careful, the utility knife will cut into the copper wire. BE CAREFUL NOT TO CUT THE WIRE.


Once the insulation is mostly off, pull the remaining bits off with a needlenose pliers.


Wrap your new wire around the splice area. Get it nice and snug against the splice area.


Put some soldering flux on the wires and heat up the soldering gun.


Apply a small amount of solder to the splice area.


Yours should look better than mine ;) Wrap it up with some electrical tape and reinstall.

[martini]

good writeup, but i would strongly recommend against pulling the pins from the connectors. I have seen so many people mess up the connectors. Those little pins can very easily bend and you need the special molex crimper to put new ones on correctly.

Although a small flathead works, there are special pin tools to pull them out without damaging them

if you are very careful. you can do it. But the pin engagement at the connectors is critical and even something that looks ok to the eye will test out of spec.


just fair warning.


I would recommend just tapping the wires as you did in step 3 - use a razor to expose the copper, and then solder - no messing with the pins needed, and the wire doesn't have to be cut.

[bananas]

good writeup, but i would strongly recommend against pulling the pins from the connectors. I have seen so many people mess up the connectors. Those little pins can very easily bend and you need the special molex crimper to put new ones on correctly.

Fair enough, I definitely value your opinon as the writeup king. However, I've pulled many pins from my ECU over the years, and have never had a problem. I do tend to be pretty careful.

[Pswish]

Any update on this, pictures no longer load?