Electrical systems have panicked more than one car builder. It can seem overwhelming, especially for builders who haven't had a grounding (see what I did there?) in electrical wiring. But it doesn't have to be that way with the SL-C.
Where do I Start?
It's often easy to understand things if you break them down into multiple parts. In the case of the SL-C, there is the wiring for the engine, and the wiring for everything else.
The interface between the two is very simple- just two wires, typically: B+, or constant battery, and switched ignition.
That means there is a clear line between how the engine is controlled, and how the rest of the car is controlled. This approach makes it easy to understand, debug and install.
Let's start with the engine first: if you are using an LS engine (and about 80% of SL-C builders choose this powerplant for reasons of power, weight, ease of installation and a broad upgrade path), there is an easy solution, which is to use the GMPP controller kits designed for your engine. These include the engine control computer, the complete engine harness with connectors already attached and labeled, a dedicated engine fusebox, a throttle pedal, O2 sensors and some other small parts. Once you install this on the engine and connect the coolant and fuel lines, just two wires separate you from a running engine. You'll spend more time thinking about where to place things than actually installing the harness and related parts- it's really pretty easy if you take your time and are careful.
For other engines, there are similar kits, notably for Ford and Chrysler crate engines. Those builders who want to go way off the reservation and install Rotary, Porsche, BMW, Maserati, Ferrari, or other engines will have a more difficult time, though there are many plug-and-play solutions for many of those engines. But however you control the engine, the interface between the engine control system and the rest of the car is likely to be the same of very similar to the GMPP controller kit approach discussed above, using just a constant battery connector and a switched ignition wire..
Luckily, the InfinityWire harness that controls the rest of the car and which comes with the kit, has just those two wires you need.
As of late 2011, the SL-C ships with a complete electrical system from InfinityWire, including wireless remotes to unlock the car and set security, the necessary Master and Powercells, and a custom harness that is designed to make the process of wiring the car to be mostly as simple as bolting up the cells, fastening the harness, and plugging the harness in to the rest of the car. You'll have to terminate a few car-specific items like connections to the fuel pump(s), etc, but the rest of the car is really extremely easy to wire.
This is a revolution in component cars, and unique to Superlite Cars. While any car can of course have the InfinityWire system fitted to it, so far only the SL-C has a custom, plug-and-play harness that is designed to do every basic function of the car as far as possible. The electrical system typically ships with the kit, and comes with a comprehensive manual that details how the system is to be installed.
The obsolete EZ Wire system can be found here.
As of 2018, SL-Cs are being shipped with a new, custom harness and alram system. More details will be provided when we have them.
Potential for More Customization
The advent of the InfinityWire system as a standard feature in the SL-C also makes it much easier for a builder to go beyond the standard setup, and add powerful features like control from an iPhone or Android device, or use of an optional 7" LCD screen to control and monitor everything happening in the system. It also means that it is easier to install more sophisticated features to the car, with additional programming on the cells, and by adding new cells, including ones that are designed to manage motor-driven features (e.g., electric handbrakes, electrically operated doors and clams, etc).
If you have needs that go beyond the default kit setup, the InfinityWire system can be expanded with more Powercells to add more loads. A total of five Powercells can be installed in the system to meet expansion needs.
There is also a CAN bus switch panel with up to 8 switches that can connect to the system with just 4 wires.
Also available from InfinityWire is an optional system called InTouchNet that adds a wifi network to your car and allows the car to be controlled from any device with a browser, like any smartphone, an iPad, etc., This is potentially a very powerful addition to the InfinityWire line and several builders have already added this functionality to their cars. One of the many advantages to this approach is the ability to completely eliminate physical switches by replacing them with virtual ones on the InTouchNet webserver.
The InfinityWire system also has an optional module called InRESERVE, which automatically shuts off the entire electrical system when battery voltage drops below a specific value. This protects your battery so you will never not be able to start your car because the battery is dead, even if you left the radio on, or the headlights on high beam overnight, etc. It also works to account for phantom or parasitic draws in the system, especially those that may have been wired directly to the battery. See the InfinityWire site for more details. If you aren't driving the SL-C daily, you need the InRESERVE option, as the standby draw of the system will kill a battery in less than a week. The use of a permanently wired battery charger is also a good idea.
So how do I install the InfinityWire system?
The kit ships with the InifnityWire system, which includes a comprehensive manual. But essentially, you mount the three powercells, lay out the harness, connect it to the headlights, tail lights, steering column, etc with the already-terminated connectors, and connect the battery, alternator and fuel pump(s). It's about as easy as possible, and the complete directions are in the manual from InfinityWire.
Chasing a Parasitic Draw
Sometimes your battery can just go flat, for no apparent reason- you didn't leave the headlights on all night, and you don't have a dome light. So what happened? You probably have a parasitic draw somewhere in the car. Here's a good discussion of what to do to chase a parasitic draw.
For those who don't know what that is, it's the current used in a system when "nothing is happening". In most cars it's pretty small, and the power used is generally to keep engine computer memory alive, or the time and settings in your radio backed up.
Here's how you can go about Chasing a parasitic draw - and fixing it!
Connectors and pigtails
Many builders find the need for connectors or pigtails that are not supplied by the kit. For example, a backup circuit isn’t part of the default harness, so if you want to include a backup light, you’ll need to connect to the backup switch connector (typically on your transaxle). The right connector can be harder to find than you might expect, but there is help. Even having a factory manual for the car from which the part came isn’t usually much help, as when they do refer to a part, it’s generally part of an expensive harness which may or may not be readily available in any case- they rarely mention a connector part number for the factory harnesses.
eBay and other sites can sometimes be a source for these, but you have to be able to know what you are looking for. Mouser and Digikey are also popular sources, but again, you generally need to know what you need ahead of time, and that isn’t always obvious.
Another source is FindPigtails.com, a site dedicated to helping you source that oddball connector or pigtail. Their website is broad, and their search is based on VIN, or the usual make-model-year kind of search, but they have a chat feature that allows you to ask questions directly that seems to be useful, and they say they access to lots more that haven’t yet made it to their website.
Choosing the right alternator
It's easy to be confused about alternators- how do you know what kind, and what capacity? Here's a page that explains it all.
Batteries, and their installation
The SL-C doesn't ship with a battery for numerous good reasons, so the builder has to choose one and install it. But what is the right size and location? This page discusses where to install a battery in the car, but the correct size is a harder question to answer. As with most complex topics, the answer is that it depends.
For most cars with high-compression LS engines, start with a battery with at least 800 Cold Cranking Amps (CCA). If you are installing lots of audio or other high-current devices in the car, consider using two batteries in parallel. Check out the numerous audio internet forums as well as Youtube for ideas about how to successfully do this.
Smaller engines can use small batteries. One good rule of thumb is to look at the car from which your engine came, or was intended, and choose that size battery. You'll have a bit of headroom that way as the SL-C normally draws less power than most modern cars.
The battery technology (lead acid, AGM or other chemistry) doesn't matter as much as the capacity (and the correct wiring), so choose what makes sense for your wallet and weight plan.
Our cars are normally not daily drivers, so they often don't get enough exercise to keep the batteries charged.
For those cars using the Infinitybox system, plan to add a permanent battery maintainer, and keep the car plugged in at all times when you aren't driving it. This will keep the battery fully charged. There are many available, with good results from the best, like CTek, which is sold as a maintainer for current Corvettes, which are also often not driven every day.
These cars need a full-time maintainer because the Infinitybox system draws a fair amount of current when just "idling". It only takes a few days of this to completely drain the battery, which generally renders it useless, and unable to hold a charge for long again. "But wait," you say- what about the Infinitybox InReserve system? It's intended to do just that, but the problem is that it turns itself off way too late, so you end up with a dead battery anyway.
An alternative to the maintainer is a heavy-duty switch that disconnects the Infinitybox system from the battery- but you have to install it, and most importantly, remember to turn it on and off whenever you park. This approach has a side benefit of acting as another layer of security.
It's vital that you have at least one of these battery maintenance solutions in place, and use it reliably, or you will find yourself becoming very friendly with your local battery store.
Many SLC owners needlessly experience poor starting, especially when the engine is hot. In most cases, this is due to a couple of causes:
Insufficient battery voltage
A sufficiently charged battery with sufficient capacity is essential for reliable starting. If you have just started to have difficulty starting the car after a period of no problems, the battery is the likely culprit. In many cases, the battery may test OK using simple tests, or rules of thumb. It a battery swap solves the problem, you know that was it. Don't be that guy who "knows" the battery is fine, and wastes time and money on other things that don't address the actual problem. According to Jay Harris:
If your battery is at 12.0 volts, that is well below 5% stored capacity, especially if you are using a gel cell or an AGM battery. Fully charged should be 12.8 to 12.9 volts.
The POWERCELLs will operate down to about 5.5 to 6.0 volts. Below that level, the outputs turn off because we cannot guarantee that the MOSFETs for the outputs will be properly turned on. At 12.0 volts, you are well into the non-linear range of the battery. If you’re running a big, high-compression LS-something, the starter motor can draw 2,000 to 2,500 amps at the instant you engage the starter solenoid. For a charged battery, the voltage will drop to 10 or 11 volts at this instant in time. If the battery is not charged properly, the battery voltage can drop down to a few volts at the instant you engage the starter. In this case, the POWERCELL will reset and turn the outputs off.
This can be exaggerated if there are any poor connections between the battery, the POWERCELL and the point where it gets connected to ground.
Along with an insufficiently charged battery, this is the leading cause of poor hot starts in the SL-C. Unfortunately, most SL-Cs are built with inadequate battery cabling, both to the ground, and from the battery to the starter. All of the SL-Cs we know about with hot start problems were able to solve them with a properly sized battery with a good charge, and cabling that was the right size, and assembled correctly.
The actual optimum cable size varies with each car, and is a function of where the battery is located, the compression of the engine, the starter, and the kinds of terminals you choose (and how they are assembled). However, a good rule of thumb is to use at a minimum 2/0 cable. For example, the standard Audi R8 starter used with the popular Graziano transaxle draws 1700 watts under load, with higher peaks. That translates to 141 amps. That normally calls for 1 or 0 gauge cable. You can go up a size with only a small cost and weight penalty to add a margin of safety, so going with a good quality 2/0 gauge cable is a safe choice.
Note that current flows in a complete circuit, so both the power AND ground cables need to be the same size.
Finally, it's a really good idea to add redundant grounds at the engine. Wire-mesh ground cables are ubiquitous in parts stores and can easily be added during the build process.
Again, from Jay Harris:
If you are having problems with starting with the Infinitybox system, check that the primary power for each Mega fuse holder is connected directly to the battery -- not to the starter cable.
Also check all of the bolted connections on the Mega holder and check your ground connections for both the POWERCELLs.
|Making the tach work with LS-series engines||The tach output on the GMPP harness often causes confusion to new builders. This note clears everything up!|
|Mounting the battery||Where to mount the battery? It's not an obvious answer. This note gives you some input.|
|Motorsports wiring techniques||Wiring a race car is more like wiring an airplane. This extensive note goes into great detail about techniques, tools and resources.|
|A 1-wire alternator is simpler, but is it better? This note shows you how to wire a 3-wire alternator in your SL-C, using the InfinityBox wiring system.|
|Using the wrong start button on a car with the Infinitybox electrical system can be a big problem. Check out this page for more details.|
|Extending the Electronic Throttle Controller (ETC) harness||The standard GMPP crate engine controller comes with a complete harness. However, it was designed for a front-engine application, so mid-engined cars like ours have it a little harder as the throttle pedal is farther from the ECU than normal. This note gives you solutions.|
|Controlling the AC compressor||Running the AC compressor at engine redline usually blows it up pretty quickly. What to do? Just read this note for some ideas.|