3/16/18 5:10 p.m.

Hey GRM, I've got a multimeter and a project with electrical issues, but I really don't know where- or HOW- to start. Do you guys know of a website or book that does a good job of teaching the ins and outs of a car's wiring harness and electrics?

M2Pilot Dork
3/16/18 5:17 p.m.

Rob Siegels Guide to European Automotive Electrical Systems may be useful.


WonkoTheSane Dork
3/16/18 5:30 p.m.

Most people learn by buying either a British car or an 80s Japanese vehicle...

3/16/18 5:34 p.m.
WonkoTheSane said:

Most people learn by buying either a British car or an 80s Japanese vehicle...

It's the latter!

BoxheadCougarTim MegaDork
3/16/18 5:41 p.m.

What is it (not) doing and what is the vehicle? Some of us might be able to help with suggestions where to start. 

iceracer UltimaDork
3/16/18 6:12 p.m.

Battery stores,  Alternator produces.   Current flows in one direction,    Volts is the push, amps is the amount.

Biggest problem is usually grounds.

3/16/18 6:15 p.m.
BoxheadCougarTim said:

What is it (not) doing and what is the vehicle? Some of us might be able to help with suggestions where to start. 

The only thing the car is "not" doing is that the 3.5mm speakers may not be working. I want to learn electrical more out of a combo of wanting to install a better sound system and to actually be able to do some interesting swaps in the future.

WOB New Reader
3/16/18 11:08 p.m.

Take what Iceracer wrote and make a it a flash card, he nailed it. When you understand how something works you can fix it. Older tractors and riding mowers are simple circuits and are good to learn on.

I will suggest that you add a good test light to your diagnostic tools. While they do not indicate the voltage they help with quick tests that indicate where in a harness you have lost power or ground. Then you can check with your meter if necessary. With that said don't probe through a wire, only into just past the sheathing. When finished use electrical tape on the areas you have lightly probed.

A few other items of note:

- Use small paper clips straightened out for back probing into connectors with your meter. People often probe into female portion of a terminal and make matters worse by creating a poor connection when the connectors are plugged back in.

-Resistance makes heat. Resistance reduces voltage and restricts amperage (volume).When you have resistance it creates heat and that makes more resistance. It is a vicious cycle.

- Fuses either blow or melt. Blowing indicates a badly shorted circuit. Melting indicates resistance increasing gradually.

-There are several styles of wiring diagrams. Learn one style at a time, it will only confuse you to attempt to learn them all at once.

- Scotch locks are for hacks. If you are mad at someone or if you enjoy being raped by a gorilla then use scotch locks.

- If you must use a wire connector such as butt connector or spade comnector use only ones that are made with heat shrink and are solder infused. It makes life easier.

- Solder connections and practice before using it on your car. Use heat shrink and self amalgamating electrical tape. Solder fills air gaps and eliminate places for corrosion to build. Solder is only bad when vibration or flexion is a concern.

Hope this helps in some way,


Trackmouse UltraDork
3/17/18 1:03 a.m.

Start by never picking up a tool or touching a car. You need to learn how to trace automotive wiring diagrams. Find some YouTube videos on tracing circuits. You need to take a cheat sheet off google images too, for automotive schematic symbols. After all, you need to know the difference between a fuse, a resistor, a motor, a diode, a ground, a load, etc. 

If you can read a diagram, you can fix ANYTHING. I mean ANYTHING. 

Once you’ve become good at tracing a simple circuit, step up to tracing a diagram for a relay. Then a diagram for a starter motor. After that, trace something really hard. 

Dont forget, when diagnosing an electrical failure, it can be: a failed component, a failed component that sends the voltage, a failed wire, or a failed ground. And rarely is it the component. Wires don’t like vibration, they usually fail at the connector. And engines vibrate. 

SkinnyG SuperDork
3/17/18 1:26 a.m.

If the circuit is intermittent, it's a connection issue.

If the circuit is possessed by the Devil, it's a grounding issue.

mazdeuce - Seth
mazdeuce - Seth Mod Squad
3/17/18 5:38 a.m.

I used to model electrical flow. Neat fact, you can create large scale electrical flow models using water modeling software  (under certain circumstances) because the equations are the same, just with different letters. This led me to teaching the basic pipes theory of electricity. 

Wires are pipes. Water flows through in one direction. Battery is a pressure tank, alternator is the pump. Bigger pipes can cary more water. Voltage is psi, amperage is volume of flow. This is why, since your car is (nominally) always 12-14V, you need different size wires. Fuses are exploding balloons. Put too much water in them and they pop before a pipe does. So what you're really dealing with is a very complex plumbing problem. In general you want to know if your pipes are "pressurized" by checking voltage. Sometimes you're looking for a faucet that's dripping when the car is off leading to losing your stored water pressure. Switches are valves. Relays are little valves that open big valves.

Now, there are a LOT of ways where this analogy breaks down, it will only get you so far, but I find that it makes electricity seem more approachable to new people. 

NOHOME UltimaDork
3/17/18 5:48 a.m.

If someone just want to learn basic automotive wiring, starting from zero, they could do worse than to go buy a hor rod wiring harness and wire it up on the  bench.  Enough solvable puzzles in the project to make all your mental lightbulbs come on by the time you are done



DrBoost MegaDork
3/17/18 7:08 a.m.

I'll recommend learning a specific task: voltage drops. 

I do tech support on automotive stuff and when I ask the person on the other end of the phone to do a voltage drop, there's typically silence on the other end. 

Its not hard to do, but can tell you a lot. 

iceracer UltimaDork
3/17/18 11:36 a.m.

In reply to mazdeuce - Seth :

I mentioned that to some people and they looked at me, Say What ?   After they thought about it,  Oh yeah.

T.J. MegaDork
3/17/18 11:53 a.m.

In reply to mazdeuce - Seth :

Thanks for posting I finally understand how pipes work,wink

93gsxturbo Dork
3/18/18 8:46 a.m.

Threads like this make me really glad I learned soldering and how to use a DMM when I was about 10 years old.  Thanks, Dad!

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