I picked up my multimeter to keep an eye on my charging system. Since then I have learned about how useful it can be for everything electrical. However, I can't find a list of readings for different circuits (ohms, volts, amps on any given circuit). I know my question is pretty vague, so I'll ask- what readings do you guys look for, on any circuit you can think of? I know, this is still vague, but I want a lot of general input.

A few different threads here have been useful enough for me to print out and keep with my manuals, my plan is to do the same with this one.

Murph.

 

Cool! :)

I just write the stuff down in my Ford Shop Manual. :)
Little notes on things like "out through the bottom" "in through the top"
"{rest it on a} digging bar over the frame" for the power steering gear.

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The resistance of the ignition wires.
My Ni wire wrapped wires are 1100 ohms +/-100 depending on length.
The carbon button in the cap and the copper coil wire on mine is 1 ohm.

The resistance of the pickup coil "stator" in the Dura Spark distributor.
Mine's 560 ohms.

Resistance of your coil's primary and secondary windings.
My Standard Motor Products coil is 1.1 and 10,000.
Supposed to be 1.0 to 2.0 and 7k to 13k. (page 23-01-13 in '75)
Primary circuit resistor ("bypass") is supposed to be 1.30 to 1.40 @ 75*F.

Doggonit I didn't write down the resistance of the spark plugs. :/
Well, it's not the actual number that counts so much as odd ones that are
way different than the rest. (center electrode to ignition wire connection)

"FMC" talks about the odd (AC?) voltage the electric choke gets. :)
(IMO, nothin' wrong with a choke a hacksaw and hoof rasp can't fix;)

How low your meter needle drops when the starter is engaged and loading
the battery. How high it goes when the engine is revved and the charging
circuit fully kicks in. Those are the two "biggies" and will get used a lot.
I read them on other people's vehicles -way more- than on my own! :)

I'd like to know what voltage your coil has on it when your engine's running.

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Even a glass faced Simpson or Triplet or Weston meter can have problems
with static, let alone a cheap plastic faced one. ;) Over the years I learned
to huff and blow on the meter face every time I got a reading I didn't like. ;)
Hardly ever wipe the dust off either.

I have my meters adjusted to be right-on-zero when they are laying flat
on their back. When they need to be stood up I compensate for that, since
the actual number (in a case like that) is less important than the change I'm
looking for. For an actual careful accurate "reading" I lay it flat on it's back
and huff 'n' blow;) on it to see the needle come to rest on zero first thing.

IMO, if a guy is going to have an old vehicle he needs to have a service
manual and a meter, just the way you'd think it's weird to not have
wrenches and screwdrivers.

From the starting and ignition systems to the lighting system vehicles are
electrical. Sometimes even the dumb ol' choke is electrical too. ;)

Alvin in AZ

 

A good multimeter can be very useful in automobile applications. If you pick up a Chilton manual for your vehicle you will find a number of tests that can be performed with a multimeter. The typically as you said it can be used to check your charging system, i.e. how much voltage the battery and alternator are putting out. I would say that amperage measurements would be the least common, since you have to connect the meter in series with the circuit. Most multimeters can only measure up to 10A unless you have a current clamp. Another very useful feature is the resistance, or ohms, measurement. There is usually a setting for diode, which allows you to check the continuity of a circuit. For example; if you have the meter on the ohms, or diode, setting and touch the probes together, you will see something like 0.001 ohms...this means you have continuity. Now apply the probes to the connections on a known good light bulb and you will get a similar measurement. If you apply the probes to a bad bulb it will usually read 1, or will give the same reading as if you were not touching the probes together. You can use this feature to check relays, fuses, wires, etc…

It's great to know the mechanical part, but it's also very helpful to be able to diagnose electrical problems too. The multimeter, an OBDII reader, and a Chilton manual will get you a long way and keep you out of the shop.

 

Good stuff so far. More...

 

I found a few articles that look pretty good:

Google: multimeter uses automotive

How to Use a Multi Meter Voltmeter
Digital Multimeters
Browser Warning

 

I really do appreciate you looking those up and posting them but you've got
to hear it somewhere... do yourself a big favor and don't buy an expensive
digital meter, there isn't a single thing they can do that an analog can't do
better.

Argued that point on a few newsgroups and in the end the digital crowd was
converted. No kidding. My own son was my first convert, I had argued it
with him off 'n' on for over a year, so was prepared to kick digital butt. ;)

Ok, danggit, there is one thing better about a digital meter...
A child can be taught to read it quicker. ;)

Alvin in AZ

 

I agree that you don't need an expensive one. For most measurements you can use a cheap DMM. I have seen them for less than $5. Regarding analog vs digital, I can personally use either, but I ditched my analog about 10 years ago.

 

Analogs have their place, and Like Alvin Said, The analogs work well for our vintage vehicles seeing that most of the trouble shooting in FOMOCO maintainance manulas are written for VOM's.

But on newer vehicles there just are some engine management circuits that VOM's just won't work, due to loading of the VOM. Seeing that most DMM's have around a 10 to 11 M ohm input.

I say both a VOM and DMM are good to have as effective test tools. Me personally I like DMM's cause I am in the electronics field, and I used to work for one of the leading Manufactures of T&ME, So I guess I am a little biased toward DMM's.

 

Hey Alvin, can you recommend a good vintage analog meter? Dropped my $12 today.

 

While I am not Alvin, but my $0.02 worth. Simpson 260-6XLM or 6XLMP are a good choice. Most Simpson meters are good, I am not too sure of what is left out there that is a quality VOM. I Have delt with and been inside some of Triplett VOM's, and am not impressed.

You can find used Simpson VOM's on ebay.

 

Thanks! I'll start searching.