How To Test Electrical Circuits / Wiring

[GLPoomobile 958]

I'm hoping that some of you can post some really good technical replies to this to serve as a future guide for numpties like me when we are searching.

 

It has to be one of the most common type of topic on this forum - alternator not working, battery draining, slow starter, dodgy earths, the old brown plug etc etc. Time after time I see replies that mention testing voltages or resistance or current etc etc, and they are often written by very knowledgable people.

 

There's just one problem........some of us don't know how to use a Multimeter, and this concise advice may often be well over our heads. Sometimes we need advice in laymens terms

 

I have a basic knowledge of electrics, but I'm afraid to say I've forgotten more than I've retained from what I learned at school, and the last time I used a Multimeter was at school too. And as I'm about to do a bit of loom rewiring, I'd like to arm myself with tools and knowledge to ensure my new wiring is up to scratch before re-connecting it all, and then wondering why the car won't run.

 

Some come on guys, lets have the replies coming. Describe in simple terms, step by step if need be, how a beginner like me should go about checking integrity of wires, voltage drop, resistance etc. All the most common tests that you might have to undertake on the typical misbehaving GTI. You all know the score

[welshpug 1,657]

the most common function I use is the continuity test, just poke the wires at the corresponding ends and if it beeps all is fine, if not theres a problem or its the wrong wire.

 

another helpfull tool is a power probe, but I havenmt got one myself yet, adn you have to be careful with modern cars not to fry stuff with 12v+ shots of power up the wrong pins...

 

I'm by no means an expert at this yet, still learning but growing in confidence especially now i've nearly completed a management swap twice.

[Mikey S 29 1 Cars]

right, help coming up.

 

most multimeters have 3 pins at the bottom of them.

 

COM is earth, your black lead should remain plugged in here.

 

VMA is where your red lead goes when you are checking for resistance, measuring voltage, continuity etc.

 

10ADC is where you would plug your red lead in when you want to measure voltage draw, drain etc.

 

to measure voltage at a component, for an example, charging rate, hold your red lead with it connected to VMA on the meter to the positive side of the battery and black lead on the negative side. this will give you an reading. you can do this for many different sensors etc to check if they are recieving or giving out the correct readings.

 

to measure continuity: take your meter and connect one probe to one end of the wire and the other probe to the other end of the wire. with the meter set to continuity, your readings on the meter should drop to 0 if it has continuity. the meter may also be fitted with a buzzer for this test. doing this test will help you trace a wire from a sensor to the ecu for example.

 

to measure resistance: meters are usually fitted with about 6 different levels of resistance, 10k, 100, etc. you will have to select which level you want according to what you are measuring. im not 100% sure about what you would chose for an ecu water temp sensor for example as my own mulitimeter is auto ranging but you should be able to work it out with the readings that you get from the meter. connect the meter into the terminals of the sensor and it will tell you the resistance. compare this to a manual to see if its within tolerance.

 

to measure drain. connect red lead to the 10ADC pin. to measure the drain on your battery for example, disconect the negative side of the battery, connect red lead to negative terminal and black to an suitable earth point. switch meter to 10A. the reading thats displayed on the meter will be what the drain is. if you think that you have an excessive drain try operating a few circuits (alarm, interior lights etc) to see if the drain drops.

 

there is alot more you can do with an meter, but the above 4 tests will help with the majority of most problems that a 205 will throw at you . even though im a technician, i dont do a massive amount of electrics, but whats above is what i do and i can overcome the majority of electrical problems that are thrown my way

 

hopefully someone can add some more so we can get it catalogued into one decent thread to help others.

 

hth

 

mike

Edited August 8, 2007 by pugger

[SPGTi 2]

Try HERE and HERE

 

Steve