A Rainbow of Wiring

"A pox on both your houses!" 

- Mercutio, Romeo & Juliet ActIII, scene1

I cannot say how much I hate wiring. Well, actually, I can...but not unless I censor it heavily for this blog.

I'm not scared of it, mind you. Dad first set me up wielding a soldering gun and made me practice making good solder joints for electronic applications when I was seven. I've been doing my own stuff for a long time and I don't think there's a car I've owned in 30 years that I didn't wire up like Hi-Fi freak's basement when it came time to put tunes in.

Automotive electrical doesn't scare me either: 2 months after I had driven my 1977 VW Scirocco coast to coast for college, I tried to start up one chilly morning and got nothing. So I started my father's classic diagnostics: "Fuel, Fire, Air." Those diags led me to pay-dirt in 2 minutes flat, which was good because I didn't even own a multi-meter at the time: Turned the key to run, and heard...nothing. I should have heard the fuel pump by the left rear wheel come on. I'd only owned the car for 5 months, but I'd read the repair manual cover-to-cover as a sleep aid. I hot-wired ("jumpered") the pump power on, confirming that the busted part was the pump relay and drove the car into town to lose a week's income for a new relay.

So I ain't 'fraid a no wires.

From 1949 VW used a pictorial style of wiring diagram and it gave you a sense of not only what the wiring path was, but also where the components were within the chassis. as well as a literal line drawing of the starter and even where to connect what wire. DIY bliss.

While busy, the diagram is readable. The components are accurately drawn, and there are no nutty surprises.

In 1973 VW changed to a schematic diagram style which showed only a common ground and symbols for the components. The diagrams went from readable to migraine inducing. I'm not the only one. I've offered them to many of my friends who are Electrical Engineers and they've stared at them and to a man, all have said, "Well, it might be accurate but this is almost impossible to read. I wouldn't want to work on a system that required using this as a guide." Uh, oh.

A part of my soul just died.

Because of the schematic style, the wipers, starter, heat blower fan, and fuel pump are all represented by the same symbol. (There's a cookie for anyone who can think of what all of these things have in common electrically.) There was a separate key published for what component each symbol represented (in case you didn't have an EE degree) and a reference to what "current track" to ground it was on. You had to click your eyes back and forth between the schematic and the key of over 100 different components to puzzle it out. There was also no sense of proportion: A switch might be located between a component and the ground and the whole line be only an inch long, but the true distance in the vehicle is a wire running all the way from the dashboard to the engine at the rear.

A raging nightmare...unreadable.

By the way, the aforementioned are, electrically speaking, motors. So they all look just the same, diagramatically:

In 1979, VW realized their mistake and began adding pictorial style components back in to the schematic diagram, even captioning some of them within the diagram. A 1979 diagram is close to my 1977, so I often consult the 1972 (pictorial), the 1977 (schematic), and the 1979 (hybrid) all to make sure that the wire I'm staring at in the half-light really is Blue/Red, and not Blue/Black that has faded with heat and time and really is supposed to be attached to the alternator idiot light.

In short, the diagram is barely readable, the color coding often insufficient to communicate meaning, and the whole harness supports a primitive EFI system (Bosch L-Jet) where the ECU is only smart enough to squirt fuel relative to air intake. Every other part of the EFI sub-system is uncoordinated from the ECU. As a systems designer, this whole thing makes my gut go cold: So many ways for it to go wrong, both catastrophically and subtly.

Now replace the engine, EFI system and uncoordinated components with a Subaru and its much smarter brain. Have a kindly Subaru wiring harness expert make trims to remove all of the unnecessary items and send the Subaru harness back to you with the admonishment: "Three wires: 12v battery, Key ON, Fuel Pump. If you can't figure out where to attach three wires to your vehicle chassis harness, I can't help you." He's right. How hard could it be?

Harder than it looks. Subaru harnesses are notorious for subtle differences from month to month, let alone from year to year and model to model. Maybe Subaru has some serious quality control issues in their wiring assembly division, because sometimes the signalling wire from the whatsit to whizgig is Blue with a White stripe...or Red with a Yellow stripe, or ....Brown. Consult the factory service manual for the model, year, trim, and market  (Impreza MY1997, Outback Sport, LHD USA) and that diagram says the wire in question should be Chartreuse with an Indigo stripe. Oh, hell.

Usually such headaches hurt less with a Subaru because everything terminates at a fitting, and every fitting is shaped so that it can only connect to a specific component. The electrons don't care what color the insulation is, so why should you? You're guaranteed that you can't plug in to the wrong place.

Until you cut the harness. Then that certitude is lost. Now try to graft it to a chassis harness designed to support an uncoordinated Solid State EFI system only slightly more complicated than a transistor radio to a reasonably modern ECU which pretty much requires 'three wires' to make it go.

The good news is that some things don't change. Both systems use the positive stud at the starter motor as the primary junction for the chassis harness, the ECU, the battery, and the alternator output. Both systems use the chassis as a common ground. Both systems use 12 volt power. The bad news is that those are where all of the similarities between the two systems ends.

My harness man is right: If you can't figure out where to hook up three wires, maybe you're in over your head. I know what the big three need to DO, I know what the electrical path is for them to do it, and I know what the switching path is (at the front of the vehicle on the other side of where you turn the key.) What I'm having trouble unravelling is VW's baffling diagram, and which parts of the factory EFI interface I can ignore, and which ones I must route around, and which ones I have to live with.

Sidebar: When it comes to systems (technological, religious, ethical, philosophical, etc.,) all of them have fundamentals that are the starting point for everything else. This reductivism is helpful, because they restrain adherents who inevitably wish to complicate it. An example would be Jesus' directive to love God first, and then love others as much as you love yourself. Others include The Five Pillars of Islam. The Four Noble Truths of Buddhism. Asimov's Three Laws of Robotics. Ken Thompson's 3 Rules of UNIX Philosophy. All systems with a limited set of starting rules. The fact that they're systems conceived for completely different purposes is irrelevant.

The T2B VW Bus electrical system has three fundamentals:

Suitable for framing, while doing VW wiring.

• Terminals #30 are ALWAYS powered, even if the key is OFF.
• Terminals #15 are only powered when the key is in the 'run' position.
• Terminals #50 are only powered when the key in the 'start' position.

Notice these are "Terminals" or connection points, not the wire in-between. It comes to the same thing as long as the wire doesn't join or branch. This should make everything much simpler. By convention (certainly not a guarantee, but good enough to guide you if you Trust But Verify) each of these is color coded:

Red is always #30 (12v, unswitched.) If you see a pure red wire, it is tapped back to the battery and is live all of the time. Other color wires may also be #30 (Red/White) so this is not a 1:1 relationship. #30 is often but not always R/R, R/R is ALWAY #30. (R/W is the trunk line power to the fuse panel and therefore, everything under the control of the driver. As soon as it joins the panel...back to RED.)

Black is always #15.  Unlike #30, #15 is always a conditional source: they key must be in 'run' to make #15 live. #15 then distributes power to other sub-connections. Find any component that only works when the key is in 'run.' Stare at the wiring diagram. Stare harder: even if you have to jump through a few conditional switches, you WILL find your way back to #15. An easy example is the back-up lighting.

#50 is always Red/Black. Thankfully, there is very little of it. It's pretty much a single wire with two ends and no branches: One at the ignition switch where it receives power from #30, and one at the starter solenoid. When you turn the key to 'start' the switch closes between #30 (R/R) and #50 (R/Bk) and the power hits the starter solenoid which pulls the starter gear into place. The starter takes care of it's own heavy Amp power switching itself. When the engine catches and you let go of the key (which falls back to 'run') #50 is disconnected and the solenoid retracts the starter gear. Now in 'run' (#15) everything that is #15 dependent is available.

Soon I'll give you a better idea of what the actual 1:1 connections are between the T2B Bus, and an OBD2 Subaru ECU. It turns out, the major challenge is knowing what to IGNORE.