Where does the truck's electrical system (the feed for the fuse panel) connect to the charging system? Is it at the battery side of the starter solenoid?

 

It is essentially connected thru a splice to the output of the alternator. The wire from the alternator to the battery side of the solenoid has the shunt connections (splice) that drives the ammeter. Most of the wiring diagrams are real confusing.

 

I'm still confused. There is a large orange wire that feeds the fuse panel. Where does this wire connect? I thought it went to the batt. side of the starter solenoid. I'll try to check later today. I wish I knew where my wiring diagram was. I'm kinda curious now.

 

Check your wiring diagram when you find it. There are two feeds to the fuse panel. One is always hot from that splice near the alternator that I spoke of. The other one comes from the Ignition switch. The devices connectioned to the battery side of the solenoid will show as a "charging" current on the ammeter providing the ammeter connections are good and it is working.

 

Ok, I see it. I still maintain that a volt meter is a better guage. Gives more information, is safer than a 'true' ammeter, is more robust, and is easer to install. When I restromodded my Mustang, the factory ammeter got pitched in favor of a good voltmeter.

Case in point:

http://hp.autometer.com/techtips/faq...erammeter.html

 

I have a 1979 F150 4X4, which came stock with an amp meter. I prefer an amp meter to a voltage gage since it will give a better indication of the health of your charging system, in some situations a voltmeter will not. For instance, I have seen diodes in alternators go bad, (Open), and in such cases, the alternator will still produce 14-15 volts, but little amperage. Meaning it will charge but not fast enough to keep up with the demand.

The amp meter is designed to indicate the flow of electrical current. If the engine in not running, and you turn on the lights, the amp meter will show that you are discharging your battery. Some meters will let you know how much discharge is being placed on the battery; a great was to test for shorted wires. When the engine is started, the amp meter will indicate how much current the alternator is putting back into the battery. When the battery is fully charged, the indicator should read near zero, meaning the battery is fully charged and the alternator is producing enough energy to take care of the truck’s needs. If the alternator goes out, the gage will show discharge, just like it does when the engine is off. If you know how to read them, they will give you more information than a voltmeter will.

Anyway, I believe the amp meter on these trucks is a shunt type system. That is, they read amperage by measuring the voltage drop across a shunt or resister. This voltage drop, usually measured in milivolts, is feed into the meter and the gage needle registers accordingly. The benefits of such a gage system are the small gage wire used to run the meter. If the meter fails to work, it could be one of 3 problems: 1. The gage is defective, 2. The shunt is defective, 3. The wiring between the shunt and the gage is defective.

It has been many years since I have troubleshoot one of these circuits, but I believe the shunt, called a resistance wire, is located in the wiring harness, near the passenger side firewall. If you trace the Red wire with a green strip coming from the alternator, you will find it. It leads to a blue wire with a green strip. Where these two wires meet is your shunt. You can check the shunt with an ohmmeter. The resistance of the shunt should be low. If the resistance is high or reads open, this may be your amp meter’s problem.

Other type amp meters, like the under-dash type are direct reading. For these meters a large diameter wire usually an 8 or 10 gage, must be connected to both sides of the amp meter. These are more simplistic and easier to troubleshoot, but harder to hook up because of the large wires.

Happy motoring,
John24255

 

If the shunt reads high resistance, the reason you ammeter isn't working would probably be that it is now burned out. If the shunt opens or goes high resistance, then that milliamps that the meter is designed for turns into several full amps. And the meter goes POP!

You are correct. The shunt is a wire in the harness between the alternator, voltage regulator, and the starter solenoid.