Book on Basic PreComputer Automotive Electrical Circuit Analysis

[lespaul]

Can anyone recommend a very basic book that teaches the very basic fundamentals of how to analyze precomputer automotive circuits and read basic wiring diagrams? Very basic -- just the fundamentals. I need to start from square one.

[irl]

I bought these two. They do go into a bit on modern systems but most of the content is the basics. I also would love to know if someone knows an old school book that they like.

http://www.amazon.com/Automotive-Wiring-Electrical-Systems-Workbench/dp/1932494871

How to Diagnose and Repair Automotive Electrical Systems (Motorbooks Workshop): Tracy Martin: 9780760320990: Amazon.com: Books

[Lapkritis]

Brad,

If you're a logical thinker then the wiring diagrams should be a quick study for you. I self-taught a number of years ago and most manufacturers and repair manuals are all very similar. There will normally be two letter abbreviations for wire color and then the gauge or thickness of wire as a decimal... then component drawings and internal relays etc that can take some time to learn. If there is a connector at the end of a span of wire, it will list the position/location on the connector where the wire lands in sequential numerical order. When you have such a connector in hand and know the position of one wire/color then you can quickly deduce the other wires on the same connector just like arriving at a 4 way intersection with road signs. A wiring diagram is just a miniature map of the strands of wire in your car.

[911pcars]

Before one can diagnose and repair, it's necessary to understand how the system works. Stay away from your vehicle schematics until you understand voltage, current flow, grounds, etc.

For basic automotive electricity, you can choose from any number of books or internet sources on basic automotive electricity. Begin with a Google search: "basic automotive electricity". Here's one basic website that looks reasonable: How car electrical systems work | How a Car Works

Read book and website reviews. Unless from an established publisher, some sources and forum opinions can intersperse facts with anecdotal assumptions.

Sherwood

[Dave Colangelo]

Diagnosing electrical problems comes in a few different manners on older cars. Since they tend to not have that many components your problems are limited.

Shorted wire, this can be in the form of melted wire casing or a wire that was pulled out of a connector some how. There are some other things that could cause this but there are the main 2 things I have found over the years to be big issues.

A bad component. In this case some kind of a sensor or unit could be bad. In these older 911's think CDI box, bad relay, blown fuse, or bad coil etc.

Low or no voltage. If your alternator/VR is bad you may not be getting the proper voltage to run the components typically 12Vish in cars

In the end of the day all you really have is components connected by wires, some that take inputs (from the engine or the driver) and some that drive outputs (the coil,tach, speedo etc.)

You are best off spending your money on a good multimeter and an oscilloscope as many of the text resources you are looking for are on the internet for free or here on the forum.

Regards
Dave

[porschenut]

Originally Posted by irl

I bought these two. They do go into a bit on modern systems but most of the content is the basics. I also would love to know if someone knows an old school book that they like.

Automotive Wiring and Electrical Systems (Workbench Series): Tony Candela: 9781932494877: Amazon.com: Books

How to Diagnose and Repair Automotive Electrical Systems (Motorbooks Workshop): Tracy Martin: 9780760320990: Amazon.com: Books

Those are the two that I bought, when I wanted a primer on car electrical systems. Excellent place to start.

[Bob Kontak]

Originally Posted by 911pcars

Before one can diagnose and repair, it's necessary to understand how the system works. Stay away from your vehicle schematics until you understand voltage, current flow, grounds, etc.

+1

I have used a multimeter with the diagrams and have found several shorts, poor connections and grounds, etc before understanding current flow.

However, I did it backwards and after years of using two functions - voltage and resistance - finally watched a couple of youtube videos that demonstrated how to use a multi-meter to check current flow/draw. I thought, "That's it? That's all it takes?"

I used the current draw function for testing the fuel pump "life". They say that brand new is six amps, eight amps is mid life and over ten it's getting long in tooth. I was skeered but I moved the wires around to the fused circuit in the MM and pulled it off.

What I don't understand is if a MM has a ten amp max current draw internally (with it's own fuse) how do you check current draw on something a little beefier?

[Algernon]

What I don't understand is if a MM has a ten amp max current draw internally (with it's own fuse) how do you check current draw on something a little beefier?
Actually, Bob, a MM with a 10A current range measures circuits that themselves have a max draw of 10A. And usually the MM has a separate "10A" range, with leads plugged in differently. This is because (unlike the other ranges) the 10A range does NOT have a fuse!!
Trying to measure more than 10A will result in burning out the MM, as there is NO fuse protection! For more than 10A (or 20A for some MMs) you need a different strategy -usually costing more, or only rated for a few seconds, like the HF high current meters. Hope this helps.

[911pcars]

Originally Posted by Algernon

What I don't understand is if a MM has a ten amp max current draw internally (with it's own fuse) how do you check current draw on something a little beefier?
Actually, Bob, a MM with a 10A current range measures circuits that themselves have a max draw of 10A. And usually the MM has a separate "10A" range, with leads plugged in differently. This is because (unlike the other ranges) the 10A range does NOT have a fuse!!
Trying to measure more than 10A will result in burning out the MM, as there is NO fuse protection! For more than 10A (or 20A for some MMs) you need a different strategy -usually costing more, or only rated for a few seconds, like the HF high current meters. Hope this helps.

A decent MM should be fuse-protected in all current modes. If not, have at it and good luck. BTW, a cartridge fuse for a Fluke meter is $10. I learned to be extra-careful after exceeding 10A.

As for measuring current levels exceeding the capacity of the meter (e.g. starter motor), here are two methods:

a) Shunt resistor. Explained here. Ohms Law confirms the calcs:
measuremenTest | test and measurement: How To Measure Current Using A Shunt Resistor

b) Clamp meter. More commonly used. Explained here:
Current clamp - Wikipedia, the free encyclopedia

Sherwood

[Bob Kontak]

Originally Posted by Algernon

And usually the MM has a separate "10A" range, with leads plugged in differently. This is because (unlike the other ranges) the 10A range does NOT have a fuse!!

Thank you. Good info. My last MM that was a decent one said 10amp "fused" for the current draw. Probably to protect the MM vs. cooking it. The pic below shows my current cheaper one and it clearly says unfused.

So I am thinking, if you want to spend the coin, you could get a hefty MM with a 20 amp fuse for current draw as well.

Does this make sense?

[tirwin]

In a previous job I used to manage an Internet network engineering group. While we focused on the networking part of the job, we had a common systems group that managed sizing the power, HVAC, etc of the equipment we selected. It was not uncommon for one piece of equipment to have four 80A rated DC power supplies. The techs always used the clamp style Fluke meters. Not cheap but worthwhile for the job.

I think the hard part with the clamp style in automotive is that some circuits it's hard to isolate just one with the clamp. The 14-pin connector comes to mind.

[porwolf]

If you want to measure greater currents than 10A with a multimeter you need an external shunt resistor. Here is the explanation how it works:



And here you can get shunt resistors:

Amazon.com: shunt resistor

[Dave Colangelo]

When it comes to higher current measuring I use dedicated meters. For what its worth there are quite a bit of vintage pieces on the market that can be had for very little that are great for this. The more budget meters out there are typically 10A or 20A (from what I have seen) and usually will go down to 1/10 of an amp with the better ones getting to 1/100 of an amp or below (good for measuring small draws).

Get a good fluke and you will forever be happy.

Regards
Dave