Power probe III don't show voltage when connected.

to get b24 volts from 2 x 12 volt batteries
connect the negative (- ) terminal of one battery to the ground point on the motor
next connect the positive terminal (+ ) of that same battery to the negative terminal of the next battery
connect the positive terminal of the last battery to the power terminal of the motor
so it will be negative to ground , positive to negative , positive to motor or motor control
(-) to ground (+ ) to (-) , (+) to motor
That is called a series connection and increases the voltage available

HI Jack,

Can you give more details? Is this a house circuit that you are working on, or some vehicle?

In either case, look thoroughly through the ground side, or common side.
With 120 volts, it is possible to have voltage present, sensed with a voltage "sniffer" (needs no direct contact, works by induction) and no go of what you are powering.. My guess is this is not the type of circuit you are working on.

With 12 volts, it is possible to have power, and read with a test light type of tester or VOM. Again, look at the ground side.

SO, another possibility is that you have a "cold" circuit. This type of failure is because of poor, damaged or corroded connections somewhere in the circuit. With this type of failure, you often can get a valid voltage reading, but the circuit fails when actual load is applied.
To find this type of failure (IN 12 VOLT systems), hook up the thingy that you are trying to power, set VOM to enough range, and check along each leg: Positive and Negative. Point to point. one end goes to Positive battery, for example, then you probe just after each POSITIVE connection, along the circuit. What you are looking for is a voltage. for example: a poor connection would have zero volts read on one side of the connection, but 2 volts just after the connection.
So, the quick way is positive battery terminal, to your device, then negative terminal to the negative on your device. One will give large reading. Investigate that 1/2 of the circuit, and you will find you issue.
Hope this helps, if not, get back to me.
Doc

The car battery has 6 cells, each cell holds 2 volts, and connected in series adds to 12 volts. Just like your flashlight, each battery hooked in series results in increased voltage. Its possible one cell is not holding a charge, which slowly drains power from adjacent cells. In battery series connection, if one cell won't hold a charge, electrons will flow to lowest cell voltage in attempt to equalize voltage. So when one cell drops to less than 2 volts, the electrons from other cells will flow to this cell to recharge and bring voltage up to equalize voltage level. To diagnose for dead cell in 6-cell car battery, remove the 6 caps to expose the electrolyte liquid AFTER you have recharged the battery for 20 minutes with 10-amp charger, or until "fully charged" indicator comes "on." With a digital voltage meter set to 5 volts DC reading, connect the negative black probe to negative side of battery and touch the liquid electrolyte with the red positive probe. The voltage meter will display the voltage reading on each cell as you move the red positive probe from one cell to another. Make a note of each voltage reading from each cell. Wait one hour or more, then take another reading of each cell. The cell that has the lowest reading is the one that's draining power from the adjacent cells. A normal battery will show no change in voltage level between the first and second reading an hour later. A defective battery will show a drop in voltage to indicate one or more cell is slowly draining power to gradually render the battery completely dead 36 hours later.

HP AC adapter, HP part number 416421-021?

http://www.amazon.com/Compatible-HP-416421-021-Adapter-Charger/dp/B0050DN8X8

Plug going from AC adapter to DC Power Jack on laptop;

Center of the plug is the Positive ( + ) connection.
This is where the red Positive probe lead of the multimeter goes.

The outside cylindrical metal shell is the Negative ( - ) connection.
This is where the black Negative probe lead of the multimeter goes.

The Function knob should be set to DC Voltage.
(Unless you have a multimeter, that automatically detects whether it is AC, or DC voltage you are testing)

If more than one scale set it to the 0 - 50 Volt scale.
You should read VERY close to 19 Volts.

[Label on AC adapter.
Output: 19V / 4.74A

19 Volts at 4.74 Amp's. (Amperes)
Don't worry about the Amperage, just the Voltage ]

For additional questions please post in a Comment.
Regards,
joecoolvette

What? Is it time to wake up?

Oh yeah, Dell Latitude CPX,

http://www.amazon.com/Dell-Latitude-Notebook-650-MHz-Pentium/dp/B00005UJYF

AC adapter example for above,

http://www.prontocharger.com/ProductDetails.asp?ProductCode=d1161

DC Power Jack example,

http://www.all-power-jack.com/Dell/Dell-Latitude-CPx.html

I see the dilemma. The plug from the AC adapter has 3 socket holes, and the DC Power Jack has 3 prongs.

DC electricity has a Positive connection, and a Negative connection.

To find out which socket holes are for Positive, and Negative, let's look again at the DC Power Jack,

http://www.all-power-jack.com/Dell/Dell-Latitude-CPx.html

The Top view shows the jack upside down, and turned around. (In relation to how it mounts on the motherboard )

The bottom left view shows the jack primarily how it sits, (Mounted), on the motherboard.

The bottom right view shows the jack turned over, laying on it's front.
Also laying over to it's right side.

Note the three prongs. (Flat bladed pins )
The one in the middle is Positive.
The two outer prongs are Negative.

Looking at the bottom Left view, the Top prong is Positive, and the two bottom prongs are Negative.

Match it up to the plug on the AC adapter cable.

Going to test the Voltage coming out? (20 Volts)
The red Positive probe lead goes into the top socket hole, in the plug.
The black Negative lead goes in either bottom socket hole.

What if I'm wrong?

A Digital multimeter will just show a negative value. -20
An Analog multimeter's needle will go down towards the 0, instead of towards 20 Volts. (DC)

Just switch the probe leads around.

For additional questions, or if I am way off base, post back in a Comment.

Regards,
joecoolvette

Hi, 1.connect the trailer connector to the vehicle connector. 2. Make sure your tester is on DC volt selection. 3. Take black test probe (usually negative) to the frame of you trailer. (You want to have a good contact with metal so you'll be able to get a good negative polarity; no rust or paint between the test probe and the metal.) 4. Turn on lights and check the DC volt between the metal frame of your trailor (black probe) and the wires which goes to the lights (red probe).
...if you got voltage (12V or 24V depending of your system voltage) it means that the bulb is gone. (you should have 12V or 24V only on one (1) wire). If you do not have any voltage on one or other wires it probably means that you got cut wires... It might be the case if it was working before.
If its a new installation make sure that voltage is coming out of the plug. (you do the same test but you place the negative probe on metal from vehicle and the red probe into the pins of the connector.)
*** In a DC system we usually get Red as Positive (+) and Black for Negative(-) ***
hope it will help

best regards

Begin by checking voltage (with a volt meter) at the battery terminals (part of the battery not the connectors). Voltage should read somewhere around 12volts (a volt above or slightly less is OK, but not lower than 11.9) Then move the positive probe to the connector and check, again, move the negative probe to the connector. Leave the probe at the positive terminal and check voltage between the block and the battery by touching the negative probe to any metal part of the block. Continue working your way down the harness on the positive side, checking volts at the power distribution center, fuses and at the main battery connection on the starter. As you get further from the battery the voltage will be slighty less but you should not see a radical drop. If you find a large drop or no volts at all where you'd expect to have a reading, stop there and find the cause.
Chances are the connections on the battery are bad and you won't have to look further than that.
If battery is not at the proper voltage, re charge it and then put the meter on both terminals and check running voltage. It should be at least 12.9 to 14 volts running and should not drop below 12.5 with all accessories on including the lights. If it does, check the alternator and drive belt.

Yes the voltmeter measures the voltage.
When you power up the computer to test the voltage on the 4 wire connectors.
Test the voltage red and balck wire should read 5 volts.
Test the voltage yellow an black wire should read 12 volts
If the burning smell is from the power supply then most likely a capacitor has blown in the switch mode power supply.
I would advise you purchase a new power supply, do not try and repair it, these mains devices can be dangerous if you don't have knowledge.

bad ground