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(I originally wrote this on a forum at "Team Chevelle")

Automotive Electrical Basics

After reading many of the excellent “Basic of Basics” topics authored and posted by “MartinSR” over in the body forum, and reading and replying to numerous posts in the electrical forum, I thought it was about time to write a “Basics” of my own.

I make no claims to being an “expert”, nor am I a professional automotive electrical specialist. To be frank, the newer cars that you have to “plug in” to diagnose are beyond what my old head can handle, but I feel I have a good knowledge of DC circuitry, and troubleshooting skills. So….

A lot of us without hesitation will completely disassemble an engine, transmission, or other intricate and precise mechanical device, repair it, and put it back together. But when it comes to why a lamp won’t light, or [multiple quote] “weird turn-signal, horn, name something” problems occur, a lot of us throw up hands in frustration. I hope this will help you to get an understanding of the elusive “Eddie Electron”, and his peculiar behavior. I’ll apologize in advance for being “too simplistic” but I write how I teach/explain. My descriptions will deal with DC circuitry, in negative ground situations.

In dealing with automotive electricals, the thing to remember is the word “circuit”. Note it’s similarity to the word “circle”! A complete DC electrical circuit MUST have the following components (at a minimum) to operate:
1) Source of Power (Battery)
2) A “To” Path (a way to get the electricity from the Source to the Load - wires.)
3) Load (a device that uses/consumes electricity – bulb, motor)
4) A “From” Path (a way to get spent electricity from the Load, back to the Source – Ground).

(It’s the same basics as internal combustion – Suck, Squeeze, Bang, Blow – if you have all 4, at the right time, it WILL run!)

Circuit 101:
In easy terms the positive/full “juice” leaves the battery (source), travels down the wire (“To” path), into the light bulb (load). The lamp uses the “juice” (load) and the negative/empty “juice” travels back (“From” path) to the battery (source) to be replenished. This makes a complete circle or circuit.
Any break or marginal connection in this circuit will result in something wrong or not working properly. It doesn’t matter what type of electrical circuit you are dealing with (lights, horn, stereo), they all have these 4 basic components.
A basic thing to remember is that BOTH paths must be of EQUAL capacity for the circuit to work properly! Example: The load asks for 150 boxes of “juice” to do its work, but has only 75 boxes worth of road (path) to send it back – the light won’t light – or it will find another road to send the boxes back (screwing up other things along the way). This brings us to the next topic, Grounding.

Ground, Grounds, or Grounding.
The cars we love/hate use a negative ground system. The negative side of the battery is attached by a cable to the body/frame of the car, and uses the frame, or steel/metal components of the car as a path back to the battery (source). The entire car becomes our “From” path back to the battery. This is why our wiring harnesses typically contain 1 wire for a given circuit.

Example: Positive juice leaves the battery or fuse block via a wire, it might go through a switch, or relay down another wire to a bulb, then….??? The base/case of the bulb is screwed into a socket, which is attached via metal contact, by bolts or friction to the metal of the car, which is attached to the negative side of the battery. A complete circuit! (An exception might be a lamp socket attached to plastic or other poor conductor – then a negative or “from” wire will be run to the nearest convenient metal object to complete the circuit.)

The problematic part of automotive electrics is usually the negative or Ground side of the circuit. It relies upon the mechanical contact between electrically conductive parts to do its job. Remember the “equal” example? If you don’t have good connections on the “from” side, the “to” side won’t work.

A good ground consists of clean metal to metal contact between parts all the way back to the negative post of the battery! This would include scraping off all paint or corrosion, putting a “star” washer (it bites into the metal) under the connection, and tightening.

Paint does not conduct electricity! Powder Coat does not conduct! Grease or Oil does not conduct! Rust/Corrosion does not conduct electricity! Twisting a bare wire around the nearest convenient screw and tightening it down does not make a good ground!

You may have spend zillions restoring your engine bay and don’t want to scratch the perfect satin black GM-correct paint, but if the ground wire/star washer from the headlight harness doesn’t bite hard into steel, expect problems!
The guys on the assembly line (and engineers) didn’t expect our objects of desire to last 30+ years. They designed and built the circuits for (guessing) a 10 year service life. “Joe 6-Pack” rams his 20,437th self-tapping screw of the week into the radiator support of the 489,783rd Chevelle that week. Back then the star washer did its job, bit into the steel and provided the conductivity needed for the circuit to work. After 30 years, billions of vibrations and years of corrosion, the connection may need attention. Remember – metal to metal contact!

On the “Positive” side
With a negative ground system, we rely upon wires to carry the positive ½ of a circuit to the “load”. The same connection practices apply here as well, but with a few precautions.

All of the “metal to metal” contact rules still apply! You must have good clean connections! The caveat is that the connection must be protected from accidental “grounding” or contact to the negative side by insulation – plastic, tape, etc. This is why the wiring or connectors are encased in rubber, plastic, or similarly protected from the ground or negative side (entire car) of the circuit.

A Break in the Action – Switches
Like the title says, that is all a switch is – a break in the circuit! A switch (in general terms) has two states – open or closed. A switch is inserted in a circuit to either enable or prevent a “load” from working. Switches can be inserted in either the positive or negative “path” of a circuit – it doesn’t matter – it still breaks the circuit! When closed current flows, when open the circuit is broken (remember the rules of a circuit). **Important** The mechanical contacts of a switch must able to equal or exceed the load of the circuit/conductors that it is inserted into!

Relays:
A relay is nothing more than a heavy duty “remote control” toggle switch. By activating a relay, you energize an electromagnetic coil that either engages or releases a set of heavy-duty contacts. You use a small device to turn a HUGE device on or off.
Example: The starting circuit. A starter solenoid is just a relay on steroids. The key switch in the dashboard or column couldn’t possibly handle the current needed to crank over your 11.5:1 BB! The switch in the column merely makes/breaks the circuit to a BIGGER heavy-duty switch that energizes the starter motor.

Fuses – Fusible links:
A fuse is a nothing more than a sacrificial element in an electrical circuit. It is a device that lives in line (like a switch, but without a choice) within a circuit, and when something goes wrong will self-destruct and save the other components. It is sized/rated for the maximum current a circuit is designed to handle (plus a bit of a cushion). If a fuse repeatedly blows, something is WRONG.


Troubleshooting:
This can get ugly. The first thing I can recommend is to take your “tried and true” probe/test light, find the biggest BFH in your toolbox, and release some anger with the hammer on the test light! Beat the darn thing into atoms with the BFH.
Now that your mind is clear, invest some bucks into a decent Digital Volt/Ohm meter. Find a unit that has a “beeper” for continuity, and a plus would be alligator clip adapters for the probes. Gift Ideas – ask for one.
Learn to use this thing! It’s a wonderful device, and it won’t blow up or smoke the circuits you’re testing the way a test-light will!

Attach the Blk/neg lead of your new Digital VOM to a good ground (re-read “good ground”) dial it to the DC Volts / 20 scale and start checking your circuit with the positive/Red probe! Nearly every circuit in our cars starts from “hot”, goes through switches or relays, to a “load”, then back to source via “ground”. Probe the +,Red, Pos. lead to each side of every device in the “chain” or circuit. It should read out between 11 and 14.00 Volts (depending on the car’s battery condition). When the meter goes OPEN, 0.0 or OL (it depends on the meter) you’ve found the problem – a break in the circuit – a defective or open part of the circuit.

The continuity “beeper” is a great tool as well. You can check fuses (that visually look good), or verifying the circuit path is intact. Example: De-energize the circuit, and set the meter to continuity/beep and touch the probes to each side of a device – if good it will beep. Follow the circuit path beeping your way along.
 

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John I've sticky-ed these post because I think the information in them can help everyone here. If you have anymore please add them as you get a chance and I'll sticky them also or maybe we'll join them into one thread, sticky that and lock it except to add additional info. People would be able to start a new thread for questions.
 

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I just dropped off my 64 for a safety look over and was told that they had never seen an electric fan on the FRONT of the radiator pushing air vice on the back side of the radiator pulling like the conventional motor mounted fan. Id there any advantage or are they just trying to sell me a puller fan? --- thanks for any comments/experiences.
 

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Thanks. Ive been having problems getting my 1981 El Camino 231 V6 3.8L to start, I just noticed that a braided wire thats connected to the firewall has broken off from the engine could this be causing a problem with the engine not starting Thanks in advace for your response.


Terry:dontknow:
 

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Not being an electrical expert I suspect the ground is there for a reason. I would clean the contact areas thoroughly for each end of the ground cable to ensure good contact then replace the cable and try again. A piece of wire of 10 to 12 gague would make a good temporary test ground wire. Good luck. :smileyb:
 

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(I originally wrote this on a forum at "Team Chevelle")

Automotive Electrical Basics

After reading many of the excellent “Basic of Basics” topics authored and posted by “MartinSR” over in the body forum, and reading and replying to numerous posts in the electrical forum, I thought it was about time to write a “Basics” of my own.

I make no claims to being an “expert”, nor am I a professional automotive electrical specialist. To be frank, the newer cars that you have to “plug in” to diagnose are beyond what my old head can handle, but I feel I have a good knowledge of DC circuitry, and troubleshooting skills. So….

A lot of us without hesitation will completely disassemble an engine, transmission, or other intricate and precise mechanical device, repair it, and put it back together. But when it comes to why a lamp won’t light, or [multiple quote] “weird turn-signal, horn, name something” problems occur, a lot of us throw up hands in frustration. I hope this will help you to get an understanding of the elusive “Eddie Electron”, and his peculiar behavior. I’ll apologize in advance for being “too simplistic” but I write how I teach/explain. My descriptions will deal with DC circuitry, in negative ground situations.

In dealing with automotive electricals, the thing to remember is the word “circuit”. Note it’s similarity to the word “circle”! A complete DC electrical circuit MUST have the following components (at a minimum) to operate:
1) Source of Power (Battery)
2) A “To” Path (a way to get the electricity from the Source to the Load - wires.)
3) Load (a device that uses/consumes electricity – bulb, motor)
4) A “From” Path (a way to get spent electricity from the Load, back to the Source – Ground).

(It’s the same basics as internal combustion – Suck, Squeeze, Bang, Blow – if you have all 4, at the right time, it WILL run!)

Circuit 101:
In easy terms the positive/full “juice” leaves the battery (source), travels down the wire (“To” path), into the light bulb (load). The lamp uses the “juice” (load) and the negative/empty “juice” travels back (“From” path) to the battery (source) to be replenished. This makes a complete circle or circuit.
Any break or marginal connection in this circuit will result in something wrong or not working properly. It doesn’t matter what type of electrical circuit you are dealing with (lights, horn, stereo), they all have these 4 basic components.
A basic thing to remember is that BOTH paths must be of EQUAL capacity for the circuit to work properly! Example: The load asks for 150 boxes of “juice” to do its work, but has only 75 boxes worth of road (path) to send it back – the light won’t light – or it will find another road to send the boxes back (screwing up other things along the way). This brings us to the next topic, Grounding.

Ground, Grounds, or Grounding.
The cars we love/hate use a negative ground system. The negative side of the battery is attached by a cable to the body/frame of the car, and uses the frame, or steel/metal components of the car as a path back to the battery (source). The entire car becomes our “From” path back to the battery. This is why our wiring harnesses typically contain 1 wire for a given circuit.

Example: Positive juice leaves the battery or fuse block via a wire, it might go through a switch, or relay down another wire to a bulb, then….??? The base/case of the bulb is screwed into a socket, which is attached via metal contact, by bolts or friction to the metal of the car, which is attached to the negative side of the battery. A complete circuit! (An exception might be a lamp socket attached to plastic or other poor conductor – then a negative or “from” wire will be run to the nearest convenient metal object to complete the circuit.)

The problematic part of automotive electrics is usually the negative or Ground side of the circuit. It relies upon the mechanical contact between electrically conductive parts to do its job. Remember the “equal” example? If you don’t have good connections on the “from” side, the “to” side won’t work.

A good ground consists of clean metal to metal contact between parts all the way back to the negative post of the battery! This would include scraping off all paint or corrosion, putting a “star” washer (it bites into the metal) under the connection, and tightening.

Paint does not conduct electricity! Powder Coat does not conduct! Grease or Oil does not conduct! Rust/Corrosion does not conduct electricity! Twisting a bare wire around the nearest convenient screw and tightening it down does not make a good ground!

You may have spend zillions restoring your engine bay and don’t want to scratch the perfect satin black GM-correct paint, but if the ground wire/star washer from the headlight harness doesn’t bite hard into steel, expect problems!
The guys on the assembly line (and engineers) didn’t expect our objects of desire to last 30+ years. They designed and built the circuits for (guessing) a 10 year service life. “Joe 6-Pack” rams his 20,437th self-tapping screw of the week into the radiator support of the 489,783rd Chevelle that week. Back then the star washer did its job, bit into the steel and provided the conductivity needed for the circuit to work. After 30 years, billions of vibrations and years of corrosion, the connection may need attention. Remember – metal to metal contact!

On the “Positive” side
With a negative ground system, we rely upon wires to carry the positive ½ of a circuit to the “load”. The same connection practices apply here as well, but with a few precautions.

All of the “metal to metal” contact rules still apply! You must have good clean connections! The caveat is that the connection must be protected from accidental “grounding” or contact to the negative side by insulation – plastic, tape, etc. This is why the wiring or connectors are encased in rubber, plastic, or similarly protected from the ground or negative side (entire car) of the circuit.

A Break in the Action – Switches
Like the title says, that is all a switch is – a break in the circuit! A switch (in general terms) has two states – open or closed. A switch is inserted in a circuit to either enable or prevent a “load” from working. Switches can be inserted in either the positive or negative “path” of a circuit – it doesn’t matter – it still breaks the circuit! When closed current flows, when open the circuit is broken (remember the rules of a circuit). Important The mechanical contacts of a switch must able to equal or exceed the load of the circuit/conductors that it is inserted into!

Relays:
A relay is nothing more than a heavy duty “remote control” toggle switch. By activating a relay, you energize an electromagnetic coil that either engages or releases a set of heavy-duty contacts. You use a small device to turn a HUGE device on or off.
Example: The starting circuit. A starter solenoid is just a relay on steroids. The key switch in the dashboard or column couldn’t possibly handle the current needed to crank over your 11.5:1 BB! The switch in the column merely makes/breaks the circuit to a BIGGER heavy-duty switch that energizes the starter motor.

Fuses – Fusible links:
A fuse is a nothing more than a sacrificial element in an electrical circuit. It is a device that lives in line (like a switch, but without a choice) within a circuit, and when something goes wrong will self-destruct and save the other components. It is sized/rated for the maximum current a circuit is designed to handle (plus a bit of a cushion). If a fuse repeatedly blows, something is WRONG.


Troubleshooting:
This can get ugly. The first thing I can recommend is to take your “tried and true” probe/test light, find the biggest BFH in your toolbox, and release some anger with the hammer on the test light! Beat the darn thing into atoms with the BFH.
Now that your mind is clear, invest some bucks into a decent Digital Volt/Ohm meter. Find a unit that has a “beeper” for continuity, and a plus would be alligator clip adapters for the probes. Gift Ideas – ask for one.
Learn to use this thing! It’s a wonderful device, and it won’t blow up or smoke the circuits you’re testing the way a test-light will!

Attach the Blk/neg lead of your new Digital VOM to a good ground (re-read “good ground”) dial it to the DC Volts / 20 scale and start checking your circuit with the positive/Red probe! Nearly every circuit in our cars starts from “hot”, goes through switches or relays, to a “load”, then back to source via “ground”. Probe the +,Red, Pos. lead to each side of every device in the “chain” or circuit. It should read out between 11 and 14.00 Volts (depending on the car’s battery condition). When the meter goes OPEN, 0.0 or OL (it depends on the meter) you’ve found the problem – a break in the circuit – a defective or open part of the circuit.

The continuity “beeper” is a great tool as well. You can check fuses (that visually look good), or verifying the circuit path is intact. Example: De-energize the circuit, and set the meter to continuity/beep and touch the probes to each side of a device – if good it will beep. Follow the circuit path beeping your way along.
Well, I'm in my 60's now, been working on vehicles for a living over 40 of those years, and never once had a test light do anything adverse other than burn out on me...oh, ran one over once but that was attributed to operator error, and a banging hangover new years day back in the 80's.
 
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