broncojunkie

I suppose plenty of us driving these old trucks are running bad cables. I suppose that would be as bad or possibly worse than checking an alternator that way.

5Rangers

Even a bad cable (unless its totally done) will allow some flow. I have always found the best way to check the alt on vehicle is a meter. Check the battery with the engine off and with it running.

memoniz

Okay, apparently I opened a can of worms about the alternator test. I am pretty much old school and have learned everything I know about working on autos by reading, trial and error, and asking on this web site. Fill me in if I am wrong, but the engine still works basically the same way as it always has for the last 100 years or so but with different abilities to accommodate the wants of people to the point of making a mobile pleasure palace. I still use a key to unlock my doors, crank the windows, and have no cruise control. At the end of the day, I just want to get to and from work without breaking down, nor have the privilege to pay a butt load of money monthly to do that. I appreciate the help I get from this site since a lot of people seem to know more about trucks than I do. I wish people would write there solutions , if they find one, instead of leaving us hanging though. My response to "Just Call me Sean" was not questioning his knowledge of the workings of an engine, it just reminded me of my dad and his military approach to raising his kids. Being married to a teacher, I've learned that encouragement is the best motivator. Unfortunately, I am my fathers' son and I am not trying to be that way with people myself.
Sorry for the rant. I do greatly appreciate the help though.

And honestly, I don't know squat about voltmeters.

5Rangers

Well.. a voltmeter is easy to operate and will give you a good test. You can check base battery volts right off the 2 terminals. Start the truck and then check again and get a base output of the alt. Then you can load it up, turn on ac, fan, lights, any other accessories and check the output with a load.

memoniz

Thanks, that part I've always understood, it's settings that always confused me. I don't know what they represent and need to take the time to figure it out. Is there one model that seems to work better? Or is that relative to how much you spend also? I've bought cheap ones and just have no confidence in them.

5Rangers

The Meter never lies. Your main concerns and where you will use the meter most of the time is the DC voltage test. You can also use its resistance (ohms) or continuity test. And you need to know which are the correct test jacks for the leads. Black is the common test lead. Here's some instructions I pulled off the internet. We have had discussion on here as to which meter is preferred, I like the Fluke and the old Simpson, but for our purposes here, usually a cheap digital multimeter will suffice.

Using a Multimeter

A multimeter is used to make various electrical measurements, such as AC and DC voltage, AC and DC current, and resistance. It is called a multimeter because it combines the functions of a voltmeter, ammeter, and ohmmeter. Multimeters may also have other functions, such as diode and continuity tests. The descriptions and pictures that follow are specific to the Fluke 73 Series III Multimeter, but other multimeters are similar. Important note: The most common mistake when using a multimeter is not switching the test leads when switching between current sensing and any other type of sensing (voltage, resistance). It is critical that the test leads be in the proper jacks for the measurement you are making.
Safety Information

• Be sure the test leads and rotary switch are in the correct position for the desired measurement.
• Never use the meter if the meter or the test leads look damaged.
• Never measure resistance in a circuit when power is applied.
• Never touch the probes to a voltage source when a test lead is plugged into the 10 A or 300 mA input jack.
• To avoid damage or injury, never use the meter on circuits that exceed 4800 watts.
• Never apply more than the rated voltage between any input jack and earth ground (600 V for the Fluke 73).
• Be careful when working with voltages above 60 V DC or 30 V AC rms. Such voltages pose a shock hazard.
• Keep your fingers behind the finger guards on the test probes when making measurements.
• To avoid false readings, which could lead to possible electric shock or personal injury, replace the battery as soon as the battery indicator appears.

Input Jacks


The black lead is always plugged into the common terminal. The red lead is plugged into the 10 A jack when measuring currents greater than 300 mA, the 300 mA jack when measuring currents less than 300 mA, and the remaining jack (V-ohms-diode) for all other measurements.
Range


The meter defaults to autorange when first turned on. You can choose a manual range in V AC, V DC, A AC, and A DC by pressing the button in the middle of the rotary dial. To return to autorange, press the button for one second.
Automatic Touch Hold Mode

The Touch Hold mode automatically captures and displays stable readings. Press the button in the center of the dial for 2 seconds while turning the meter on. When the meter captures a new input, it beeps and a new reading is displayed. To manually force a new measurement to be held, press the center button. To exit the Touch Hold mode, turn the meter off. Note: stray voltages can produce a new reading.
Warning: To avoid electric shock, do not use the Touch Hold to determine if a circuit with high voltage is dead. The Touch Hold mode will not capture unstable or noisy readings.


AC and DC Voltage


Resistance


Turn off the power and discharge all capacitors. An external voltage across a component will give invalid resistance readings.
Diode Test


Continuity Test


This mode is used to check if two points are electrically connected. It is often used to verify connectors. If continuity exists (resistance less than 210 ohms), the beeper sounds continuously. The meter beeps twice if it is in the Touch Hold mode.
Current

Warning: To avoid injury, do not attempt a current measurement if the open circuit voltage is above the rated voltage of the meter. To avoid blowing an input fuse, use the 10 A jack until you are sure that the current is less than 300 mA.
Turn off power to the circuit. Break the circuit. (For circuits of more than 10 amps, use a current clamp.) Put the meter in series with the circuit as shown and turn power on.

fordtrucknut

pulling the cable is fine to do IF your driving a vehicle from the early 80's or older, before the massive draw that newer vehicles require, along with the delicate computer control systems that can be destroyed by spikes in power.

southernyankey1

My experience with vehicles has taught me to ALWAYS ditch the stock cables and upgrade to the heaviest copper cables I can afford. This cuts out most of the resistance between the alternator and the battery and the starter, which means less work for the charging and starting circuits which means less heat and a GREATLY improved service life. I went through 3 alternators in a month until i ripped out the 20 year old stock cables and put in some montster 5/8 " copper I salvaged from a generator job. My truck will crank forever without overheating the solenoid and the battery has so far outlived it's normal span by 18 months and counting! A 20 year old engine harness is bound to have some corroded contacts somewhere...all it takes is one bad ground on these trucks to give you a very severe headache! You don't need to be an electrical engineer to diagnose these systems...anything under 14 volts and you have a problem somewhere...it's usually in the main cables..