After some delay I have finally been able to complete another post. With my half marathon training ramping up and the Formula 1 season starting, it was not an easy feat to find the time.

In the previous post Aftermarket Alarm Mapping, I discussed the aftermarket alarm that was installed and how it tied into the factory wiring. I have now removed all the aftermarket wiring, boxes, relays, and support equipment. A good couple pounds of junk removed.

The next challenge was to repair all of the factory wiring that was cut, spliced, or had the insulation removed. For the wires that had the insulation removed but none of the copper strands damages, I wanted to re-insulate the wire while creating a good environment resistant seal. Most people will reach for the electrical tape to accomplish this but I am not a fan of that idea. Just like I have found with the wires I removed, electrical tape gets brittle over time and the adhesive will break down and eventually let go. Searching the web and speaking to people that work in the electrical industry, I found self-fusing tape recommended several times. The self-fusing tape will create a tight seal that will not become brittle over time. In fact, the Air Force will use something similar when performing field repairs of damaged wire insulation. Since the wires I am working with are a small gage, it was important to find tape that is fairly thin to start with. I found Nashua Stretch & Seal self- fusing silicon tape at Home Depot which fit the bill.

To clean the wire and surrounding insulation I ended up using acetone, as it dissolved the adhesive from the old electrical tape really well. The key with the self-fusing tape is to wrap the wire while overlapping with each wrap. While wrapping, the tape can be stretched to create a tighter, smoother seal. I cut thin strips of the tape, as it came in a one inch wide roll, and cut the end corners to help start and finish the wrap. It is best to start and end the wraps with at least two wraps on the undamaged insulation. This will help ensure the tape will not slip off exposing the copper strands. One thing I learned when repairing several wires next to each other, is that the self-fusing tape will stick to any self-fusing tape near it. To keep this from happening I wrapped one layer of electrical tape around the self-fusing tape if it was adjacent to another repair. I guess we can never really get away from electrical tape.

For the wires that had damaged copper strands, I decided to repair them by cutting out the section. These wires I ended up repairing the same way as any other wires that were cut; using butt splices. The common approach is to buy simple butt splices at the auto parts store, but this is not the best approach for long term maintenance free repairs. With a butt splice, as with many other splices, the wire is crimped in a barrel. This holds the wire in place and ensures electrical continuity, and if crimped properly, it is unlikely the wire will come free. The issue lies at the interface between the edge of the crimp inside the barrel and wire. Over time, whether due to movement or vibration, the wire will bend at this location because the barrel is very stiff while the wire is not. Because of this stress, the wire will eventually fatigue and strands will break one by one. The solution to this is to “stress relieve” the wire by using heat shrink or a crimp that incorporates heat shrink in the assembly. The heat shrink will seal off the connection from the elements while adhering to the wire. This way, if the wire is pulled on or bent, the heat shrink will soften the interface between the crimp and the wire and help prevent damage to the strands. I still choose to stay away from the heat shrink crimps found at most auto parts stores as I have found the shrink material is usually too short and also cracks over time. The butt splices I like to rely on are the aerospace grade splices, MIL-S-81824. These are more expensive but the crimp barrel is made of a higher quality material and more importantly, the shrink sleeving is designed to protect the wire from failure.

When picking a crimp size for the wires, it is important to understand what size wire is being used. This is denoted on the Porsche electrical diagram with an X.X number, usually near the connection point or harness. Porsche uses metric wire sizes which are designated in mm², not mm diameter.

This can be easily converted using tables that can be found online. When splicing two wires together, one wire on each end, choosing a butt splice is simple as they tend to be sold with designed wire sizes. Basically find the mm² size, convert to AWG (American Wire Gauge), purchase splice with matching or lower number AWG. Keep in mind that the larger the AWG number, the smaller the wire is. When splicing more than two wires together, a different measurement needs to be used as the AWG values cannot be simply added together. Each splice also should have a CMA (circular mil area) value on it as well. This value designates the cross sectional area of wire that can be used on each end of the splice. The mm² value is already a cross sectional area measurement and it can be added together like CMA. If crimping more than one wire on each splice end, the mm² of those wires needs to be added, converted to CMA, and then an appropriate splice that fits that CMA used. Some splices already have mm² values on the packaging or specification sheet, making it even easier. Using an incorrect splice size can cause issues with crimping/securing the wires and increased resistance which can generate excessive heat or circuit resistance issue in modern heavily computer controlled vehicles.

One of the more critical harnesses that needed a wire splice repair was located at the ignition. This wire was spliced for the primary ignition immobilizer. This should have been a fairly easy wire to repair but because of the short length of the harness and the location, there was no way to get any pliers in the tight space to crimp the splice. In addition, due to the short length of the harness, there was no slack in the wire to pull them close enough together to crimp. I decided to remove the harness and repair on the bench.

To lengthen the wire to allow for a proper splice, I had to purchase wire to splice in, which opens up a debate on wire choices. Once again I try to steer clear or generic auto parts store wire. Selecting the correct AWG size is a good first step but it does not designate the quality of the wire strands or the insulation. The quality of the copper used is very important as impurities, such as oxygen, can make the wire brittle and prone to failure over time. I rely of aerospace grade wire when possible, such as unshielded MIL-W-22759/16 from Aircraft Spruce. In a pinch, when I need easy access to wire, I will use marine grade wire such as wire from Ancor, which I can purchase locally. The one down side I have experienced with marine wire is that the insulation is very thick and not as uniform in thickness as the MIL spec wire.

 

When repairing the ignition harness I added a small service loop of extra wire to ensure I don’t over stress the wire at the crimp. I have seen people try to jam a short piece of wire in between crimps to save space which only causes problems. For this larger gauge wire, the butt splices do not always come paired with shrink insulation and required the use of separate shrink wrap to stress relieve the connection.

When repairing the wiring at the door switches I learned something new about the Porsche electrical diagrams. Throughout the diagrams there are connection points, which are usually denoted by a box with a number and a couple wires leading into it. I did not know what physical connection they resembled, although now it is clear it is a basic crimp connection. In fact, when reading through the 968 Service Information Technik, I found an image of these connections. This explains the crimp splices I found at the alarm harness. I initially suspected they were from a previous alarm but it turns out it is factory.

For the connection point at the driver’s door switches, the installer of the alarm system used some sort of solder crimp joint to accomplish this connection. It actually appeared to be very solid but needed to be removed to fix the wiring. I decided to use a larger butt splice to accomplish this connection.

With all the factory wiring fixed I can now move onto the heater core removal and all the work in the engine bay that awaits me.