Deciphering Wiring Diagrams or Basic Electronics

[Kevin Whiteley]

I have been reviewing the wiring schematics for my 68 and while I have some automobile wiring experience, I don't understand solenoids, relays, horn relay, and especially the voltage regulator. I know WHAT they do, but not how they are wired or their current flow.

For example, for the 68 wiring diagram, a 2 G wire from the battery contacts the solenoid at what I'll call the 12 o'clock position. There are terminals at 9 and 3 o'clock. If it's positive going in at 12, what charge exits or enters at 3 and 9?

The above is only an example, I ultimately want to map the current flow for the whole system, so I understand better, without getting a Ph.D. in electrical engineering.

[Michael H.]

Re: Deciphering Wiring Diagrams or Basic Electroni

Unless it says "Ground" it is hot at some point. Relays are simple remote switches that close a circuit using electromagnets. For instance, older cars had a hot lead running to the headlight switch down to headlights - that's a long way for a lot of current to run. With a relay installed the headlight switch closes the headlight circuit remotely with a low current circuit - safer and easier. A solenoid is an electro-mechanical device that uses the force of an electromagnet to push out a spinning gear that engages the flywheel.

[Mike Cobine]

Re: Deciphering Wiring Diagrams or Basic Electroni

You picked possibly the most complicated item to start with. The solenoid is unique in that very little comes out, at least into the wiring diagram.

If you are looking at the solenoid from the from of the engine, you have terminals at 12, 3, 6, and 9 o'clock. The one at 12 is a large stud and nut. The ones at 3 and 9 are small studs and nuts. The one at 6 has a metal tap connected to the starter.

12 - This is the battery input. All the current to run the starter comes through this large battery cable.

3 - This is ignition switch input. This activates the solenoid. It comes from the ignition switch when you have it in the start position. Usually a purple wire on old Chevies.

9 - This is output. On older cars with points, a resistor is between the 12 v source and the coil to limit coil primary voltage to around 3 v. This is to help prevent burning the points. However, to start, you want as hot of a spark as possible, so during the starting period, a full 12 v is switched by the solenoid to the+ of the coil.

6 - This is output. It is the full current load going to the starter. It is the copper tap connection to the starter.

[Kevin Whiteley]

Re: Deciphering Wiring Diagrams or Basic Electroni

Mike,

OK, I'm getting this. Good explanation. On the diagram, I see 4 wires. The 2G coming directly from the battery. I'm guessing this is the source to power the solenoid, when the ignition is in start. That said, in "start", the purple wire is hot, and when NOT in "start", the purple wire is dead?

Essentially, the ignition is receiving voltage from a source and transferring it to the purple wire when in "start". So where does the voltage come from at the ignition switch. My diagram (and I know reading and experiencing are two different subjects) shows a brown wire also connected to the 12 o'clock pole going directly to the ammeter, with a split going to the horn relay. There is a wire connected to the 9 o'clock (yellow in diagram) that goes to the + terminal on the coil. If no current is coming in at 3 (the purple wire), is current flowing out at 9? Essentially, is 9 o'clock dependent on the 3 o'clock input or is 9 o'clock also always hot?

Basically, there are some components which operate only when the engine is running and some components which are always on. What is the closest sub-component source (besides the battery) which provides voltage to the always on items?

I know this is a detailed subject and this may not be the appropriate forum for this, but I'm just looking to get a basic handle on the electric system. Thanks for all input.

[Terry M.]

Re: Deciphering Wiring Diagrams or Basic Electroni

Kevin,
The Factory Service Manual for your Corvette has descriptions and diagrams of the operation of the starting system, charging system, and ignition system. Depending on the year of your Corvette, (generally beginning with the last half of the 1970s) it may also have schematic diagrams which show the internal circuitry of components such as relays, switches, etc.
For your 1968 you will find this information in the Chassis Service Manual. The Chassis Overhaul Manual deals with disassembly of major components one they are removed from the car - engine, transmission, differential, brakes, etc. These books are an invaluable addition to your reference library, and can be purchased from the "NCRS store." Click on the button at the top of the page.
I'm not trying to discourage your questions - just pointing you to sources of additional information.

[Mike Cobine]

Re: Deciphering Wiring Diagrams or Basic Electroni

Only two items supply voltage - the battery and the alternator. When the car is running, both supply as needed to maintain current flow.

On some cars, a second wire comes from the + post of the battery and goes to a junction block, often the engine side firewall bulkhead connector.

In other cars, this comes from the same connection as the battery cable at 12 o'clock on the starter solenoid.

the bulkhead connector then supplies voltage to the fuse block inside which distributes it to many circuits. Some are hot all the time and others are not. This also supplies the ignition switch.

Teh ignition switch is set up to basically supply voltage in three conditions: accessory, on, and start.

In accessory, it supplies to some interal accessories like the radio.

In on, the whole car is supplied if it were off before, other than the starter.

In start, voltage is supplied to the solenoid which switches the connection from the battery cable to the starter to make it turn AND to physically push the starter gear into meshing with the flywheel. It lasts only as long as the spring-loaded ignition switch is held in the start position.

This is highly over-simplified. There are many junctions, fuses, switches, fusible links, and more scattered throughout the car.

If this were a race car, it could be handled with three switches and very few wires. However, most of us like cars with wipers, power windows, lights, radios, charging systems, dash lights, and so on. And as such, the wiring diagram is quite complicated.

The main emphasis of the wiring diagram is not so much to trace current flow (you can if you have all day) but to ensure you have the correct wires connected to the correct item. Unless someone has made their own harness, it will take care of itself from that point.

[Wayne W.]

Re: Deciphering Wiring Diagrams or Basic Electroni

Frankly, I think that its nuts to try to educate someone on general electronics in this forum. I have a wall full of electronics text books and years of EE classes. Sounds like its time to go to a trade school and take a few courses.

[Chuck R.]

Re: Nice explanation Mike

Even a knuckle dragger like me could understand what you were saying

[Chuck S.]

Yeah, I Agree...NUTS!

But, taking a few electrical courses would only be effective for me if I was inside the artic circle with no television, no newspapers or magazines, no video games, no MP3 players, no bars, few associates, AND NO WAY TO GET OUT.

My attitude: Got an electrical problem?...Give it to somebody else (Ask Wayne! ). For me, reading wiring diagrams is the alternative of last resort, and certainly not where I desire expertise.

[Jack H.]

You won't need a PHd....

in electrical engineering to get from where you are to where you want to be, but a batchelor's degree or a trade degree (electronic technician) is a definite help! You see the documentation you have in your AIM or shop manual was intentionally intended to be less than a full disclosure vehicle. It's called a wiring diagram and this is NOT a schematic diagram. What's the difference?

A wiring diagram shows how various 'black box' components are interconnected for the purpose of detecting wiring faults and as a general assist in repair based on component substitution. This implies you have an 'infinite supply' of known-good replacement sub-assemblies to swap in/out to effect repair.

A schematic diagram shows what you want. It breaks open the internal function of each and every sub-assy giving you full disclosure of how things work. Reading a schematic diagram requires a basic understanding of electrical/electronic components and their international symbol designations. It allows one skilled in the art to devise go/no-go tests at the sub-assy level, effect sub-assy repair and adjustment, and it facilitates reverse engineering.

Obviously, the General didn't want to put that much information in the public domain and they only published wiring diagrams.... Those who were on the 'inside' (Chevy dealership mechanics, independent AC-Delco/United Delco dealers, Etc.) DID have access to full disclosure because it was needed in their line of work (repairing radios, Etc.).

Those of us with basic automotive knowledge and those of us with formal education in electrical/electronic work can 'muddle' by with a wiring diagram, but it really helps to have schematics especially now that off-the-shelf, factory original, service replacement parts are scarce. With a BSEE and masters + over 20-years of experience at places like Texas Instruments, I have to admit that I'm sometimes stymied in solving a given problem due to the lack of full disclosure!

Therefore, I fully agree with Wayne Womble.... What you're after; a quick and dirty complete/full education on your 1968 Corvette's electrical system is beyond the capacity of this discussion board to render.

Now, if you'd picked a Corvette of a later vintage ('75 and later era), you'd find there IS full technical disclosure from Chevy. There, the electrical content of the vehicles became dominant and a series of books were made available to the public; ST-359 series. A copy of ST-359-76 for example gives FULL schematic diagrams for the electrical systems of all 1976 Chevy passenger cars including Corvette. Unfortunately, the General didn't deem it worthwhile to spend engineering resources retroactively to document prior build cars to the general public....

Last, if electrical/electronic skills aren't your cup of tea, here's a trick that works well. Ask a cop.

A cop, why? Well, most police cars are outfitted with a wide range of aftermarket electrical items and done so at the local level. In most major metro areas you'll find an automotive electric shop that specializes in building and maintaining police cars. They're usually the low bidder to city/state competitive contract awards. This means they're CRACK at what they do and are honest to boot! Most of these shops can tackle a diagnostic/repair job on an ordinary car in record time at VERY reasonable cost....