OK, so I know I sould know this but...

Is the Alternator Gauge (talking about the actual gauge, not the light) in our trucks (1967 thru 1972) a Volt Meter or a Amp Meter?????

Thanks in advance.

 

An ammeter has a 0 in the middle, with a -30 to the left, and +30 to the right. The needle normally points to the middle when the charging system is stable, or the truck is off, and swings to the left when a load is applied, as during cranking or when headlights are turned on, and swings to the left when charging.
A voltmeter will have numbers from 0 or so up to about 18. It will normally point in the 10-14 range when the truck is running.

 

Thanks picker.

My gauge shows a "D" (discharge) to the left and a "C" (charge)to the right, so it is possible that it could be either. The wires coming off of the back of my gauge is Red and Yellow. The wiring diagram I have does not show a schematic for the gauge, only the light.

 

You have an Ammeter. Ampereage and vOltage are often confused. Without going in to electrons and theory, think of it this way-
Amps are how you measure how much electricity is flowing through a wire or any other electrical device.
Voltage is how intense that electricity is.

If you have a water hose that has 200 PSI hooked to it, that would be like voltage. It's there, but it's not moving.
If you squeeze the nozzle and let the water flow out, that would be current (amps).

Electrical power is made up of volts and amps, if you didn't have both you couldn't do any work with it, like if you squeezed the hose nozzle and nothing came out, or if the water came out but not any harder than you could squirt with a Windex bottle.
If your electrical system is working properly, Your needle should not lean towards the D, which would be discharging, unless you had a heavy load like a winch running. You should see the gauge lean towards the C most of the time, which is charging. If you turn on several loads like wipers, lights, fan motor, etc, your system should be more towards the C to put energy back into the battery as it's being taken out, but if there's more electrical demand than the alternator is supplying, you will show a discharge.
Most of the time though, your needle should be almost in the middle while driving, but just a little towards the C.
Is that clear as mud?? If it doesn't make sense I'll be happy to explain further, but electricity is a very complex subject, don't be disappointed if you don't get it right off the bat. It took me YEARS to grasp just the basics.

 

OK, this is confusing -




I deleted this post as I was wrong - will post again when I understand the wiring diagram.

 

Wow, learned something myself. The wiring diagram in the 1972 shop manual shows that it is an ammeter. Electrically speaking it goes between the battery post on the alternator and the battery post of the starter relay, with the current for the hot lead to the ignition switch going through it.

There is a shunt wire that is used only if a shunt type ammeter is used, and the wires are different if a indicator light is used. The book does not give the color of the wires.

 

You are correct sir.
The ammeter is between the battery and the alternator. Current from the alternator flows through the ammeter in one direction ( left to right in your diagram) when the system is charging properly. This is + amperage or in the "C" area of the meter.
Current can also flow the opposite direction when the battery is stronger than the alternator (charging problem or excessive load). This will show as a - amperage or in the "D" portion of the ammeter.
One of the drawbacks to ammeters is that when a device uses a lot of current, it has to pass through the ammeter. If the ammeter fails then the electrical path is broken and the device loses power. It also means that at times there is alot of energy flowing through your dash.
Voltmeters don't have this drawback. They can show you how strong the electricity in your battery is, but they can't tell you if your charging system has failed until the battery starts to lose it's energy. The advantage to the voltmeter is that it's basically just taking a reading, and practically no current passes through it. This keeps the big wires out under the hood where they belong.

 

Thanks a bunch you guys. Would it be possible to splice in an inline fuse to protect the Amp Meter? If so what size fuse would I use. I want to do all I can to protect the new wiring harness.

Thanks again for all the help.

 

It would be possible, but I would suggest a self-resetting circuit breaker. You probably have a fusible link in the system already, but once they trip, you have to replace them. A circuit breaker can also be had that has a manual reset button.
Any type of fuse, breaker, or link will give maximum protection when it is installed closest to the power source.
I can't say that I know what size breaker or fuse would be appropriate. Just guessing I would say in the 60 amp range. Be sure that each individual circuit also has it's own protection.
Don't install it betwen the positive battery post and the starter solenoid. Your starter motor can draw a lot of current and it will trip almost every time. You might consider going off of the starter solenoid terminal that th battery + is hooked to. Place the breaker there and then run the factory fusible links off the other side of that breaker.
If the purpose of the breaker is to protect the ammeter, I don't think that's necessary.
Voltage (intensity)will change as it goes through a conductor or devices, Current (flow) however will stay the same all the way through the circuit. If you prevent excessive current at the starter solenoid hot post, which is your power source. the ammeter is protected.
One option to consider would be to take the two wires that connect to the ammeter. and splice them together. Yor ammeter will no longer work. Instead use a voltmeter in it's place and tie in the + lead to an ACC or Run circuit, then ground the other lead. IMO this is safer and a bad voltmeter eill not disable your charging system, but a bad ammeter will.
There's no one right way, but there are a lot of options to consider. BTW where did you get your new harness?

 

The harness is from Painless. I want to make sure that I do not burn up my new harness. I was not too concerned until I started reading about ford placing a shunt in the original harness. I most likely will call painless for their opinion.

Thanks for all the help.

 

I have installed a few "painless" harnesses. I have had some level of defect or problem with them all. Not everyone else has.
The shunt is basically a resistor. It allows current flow through it, but it consumes some power in the process. Since the current stay the same throughout the circuit, the voltage must change. The voltage on one side of the shunt will be slightly different than onthe other side. This difference in voltage is called a voltage drop. A shunt style ammeter is technically a voltmeter that is reading the difference in voltage across the shunt. This voltage moves the needle of the ammeter and indicates amps, but it's really looking at voltage and doing some math to indicate what the current must be.
I won't try to confuse you but the most basic formula for electricity is Ohms Law:

voltage (e) = current (i) x resistance (r)

So if you know the resistance value of the shunt, and you know the voltage across the shunt, you can solve for the amperage. That's how your shunt works.

If you have no shunt in your harness, you can use an ammeter designed for no shunt and install it in the same location as the above diagram.

One more recommendation- When getting ready to test you new harness, don't use a full size battery. If theres a mmistake you could do some damage. Use a 12 volt trickle charger or a current limited power supply that won't have enough power to start a fire.

 

I see the Indian still sees the Eagle flying over the Range(!)

 

With an ampeter circuit you can start a fire if its done wrong. I switched to a voltmeter when I rewired mine.

 

That brings up a question on a friends 68 CS. The dash gauge only moves maximum of one needle width at idle 550 rpm's with lights on vs lights off at 2,500 rpm's. Such a small amount and this can be in the mornings after a cold cranking start. Alternator checks out good at 52 amps, he changed two new regulators, shows charging at 13.7 volts. Any ideas why gauge needle doesn't sweep more?

.....=o&o>.....

 

Beemer, if I read the drawing correct, it is the voltage drop across the shunt wire that produces the reading. If the shunt wire has been changed to a standard wire it will drop less voltage, thus read low. The same is true if the shunt wire has changed resistance.