Electrical Overview

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Amskeptic
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Electrical Overview

Post by Amskeptic » Sun Sep 03, 2006 8:56 pm

This may be our most challenging forum. The fact that electricity is rarely seen makes it difficult to visualize what is happening or not happening in our cars, and when we do see it, it is usually scary.

Consider electricity in your Volkswagen as nothing more than a convenient way to distribute the engine's power to other items we like to use. Engine rotation > headlamp illumination? Pretty cool.

Electricity can be visualized to useful effect by means of a water metaphor. Wires are the "pipes" and the entire body of the car is the reservoir where the electricity is dumped after doing its job. The battery is the water tower that stores the water pressure energy that drives your components. The generator or alternator shoves water up into the tower if it is not full, otherwise it sends pressure directly into the pipes as necessary.

Electrical problems revolve around clogged pipes (bad connections) or huge leaks (short circuits) or plugged pipes (open circuits) or a bad pump that lets the water tower drain down, or even a bad water tower that drains down no matter what the pump tries to do.

We have pressure (voltage) and we have flow (amperage) that describes the work it can perform (wattage). We can have good pressure and lousy flow through bad connections, that's high resistance. We can have lousy pressure and seriously good flow, that's a dying battery with a short circuit making it worse. We can have a huge leak that doesn't cause a flood (because it is not really water) but it will cause a fire (because electrical flow can heat up dramatically) a short circuit is a dangerous thing. A plugged pipe is common, in electrical parlance that is an open circuit like a disconnected wire or a burned out component.

Electrical diagrams are just the map of the city's water supply. There are street notations (wire colors), reservoir inlets (grounds), and there are little gates and switches and whatnot which we will describe in detail when I get a chance to draw them up. VW uses a common-to-German-cars nomenclature to describe certain "streets."
30, water's always on (hot)
15, water only flows when you have turned the ignition on (ignition)
(these circuits can extend all over the car as necessary)
50, only during starting.

Please note that German cars have black wire for (+) positive to battery and other components such as the coil (+), and exposed braided cable or brown (denotes "Earth") wire for (-) .

An electrical component can play possum (dead) for a couple of different reasons.
a) no pressure as in no power
b) plugged pipe as in plenty of pressure but it can't flow
c) pressure on both sides of the component, no flow again

a) your tester shows no voltage
b) your tester shows voltage but the thing doesn't work because of a broken wire to ground
c) this maddening scenario is when you have positive voltage getting fed to the ground side, both the + and the - have voltage, goofy but fixable.

The earlier diagrams laid out each wire in a laborious-to-follow patchwork over an outline of the car with readily visible headlamps and taillamps and even a battery and generator. The cars got a little too complicated in August of 1971, I think it was the introduction of the heater blower circuit.

Anyways, they switched to the significantly easier "ladder diagram" for the 1973 model year. You begin your use of this diagram with the master index for that model year. In the list is every single electrical component in your VW. Don't freak! The diagram is a pussycat to use.

Let's say that your car plays totally fricken dead one day. You turn the ignition switch on, and everything is dark and lifeless. "Gee, must be a dead battery," you say. Like a moron, you try to remove the positive post first and get a shower of sparks rivalling the space shuttle engine's ignition sequence. "Gee," you think, "this is not a dead battery."
But you are not a moron, so you open up your Bentley manual to the electrical diagram for your model year and find the master index. You look for "battery". There it is, A . Then you look at the diagram, and you see this sandwich of barcode stripes with an A next to it. That is the battery using an extra-Real Electrikal Symbol instead of some silly picture of a battery with battery caps like those early VW owners have to use. Notice that there is a big thick line going straight down to a line that runs all along the bottom of the diagram. That is the metal of your car, the "earth", the "ground" where every single electrical circuit must flow to get back to the "water tower". There are numbers all along the line that are there just for your convenience, they are called "current tracks" and they do not exist in real life. They are just there for you to find your part up above the number somewhere. There may be extraneous garbage crossing your current track, ignore it. The battery apparently is on current track 7 for a 1973 bus. The starter is listed as on current tracks 8 and 9. You notice that the big black battery cable going up doglegs over to the starter B. "Yeah, I know that," you say brightly. There is a terminal 30 (hot . . . well duh, it is right from the battery) and there are a bunch of wires coming from that 30 terminal on the starter where you have to use a 13mm nut to sandwich them all on. Because you like candy canes, you look at the red/white wire going up and banging a right along the top. "What's an S9", you ask the master index. Fuses? That is fuse #9? And that little black line that goes over to S8? It is a buss bar. The battery feeds both fuses at the top of the picture, the protected circuits come out the bottom. "Hey. S8 goes to the ignition switch at current track 16 and everything is all dead so I will check the fuse." Fuse is good. And you note that the #9 fuses is fine too. So you get out your test light with the probe and alligator clip. You ground the alligator clip on any bare metal you can find, like the ground terminal farm an inch away from the fuse box. No juice, at either fuse top of the fuse or the bottom of the fuse. Where would you go look now? At the starter? Where you accidentally left the red/white wire with the ring terminal off yesterday when you were cleaning up the connections at the solenoid?

If you have a problem with any electrical component, find it in the master index. Go to the current track listed right next to it. Go find it on the ladder diagram. Follow the wires up and you are going towards the supply the battery. Follow the wires down and you are tracing the ground path. Read the "how to use the ladder diagram" in the front of your Bentley. If you have further questions, shoot me a PM and I will try to incorporate your question right here.
Colin 01-02-11

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Amskeptic
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Re: Electrical Overview

Post by Amskeptic » Fri Dec 21, 2012 5:41 pm

Amskeptic wrote: If you have further questions, ask it here and we will incorporate your questions right here. Please allow editing for brevity.
Colin 01-02-11
updated 12-21-12 [the latest (was it Mayan Calendar?) "end of the world" didn't happen, so I have some unexpected additional time]
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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