While starting to make connections on the wire harness, the directions have two different ways to connect the voltmeter and the ammeter. What is the original gauge considered? Also, what side would be positive and which is negative? I have one yellow wire to one post and a red wire to the other. That part of the harness is still original style. The colors are stamped into the back of the cluster. Thanks!

 

The original guage is a shunt type ammeter. The shunt used is also the fuse link between the alt. and battery. The red wire is on the battery side and the yellow wire is on the alt. side. When the alt. is charging, both wires are positive but the yellow wire is more positive than the red wire by a few millivolts.

 

It is an ammeter, and like Barry said, these trucks use a shunt type ammeter circut. What I understand is that the shunt is basically a small wire that runs parallel with a much heavier wire that carries current from the battery to the ignition switch. Somewhere on this heavy wire the alternator charge wire tees-in. Somewhere between that point and the battery is where that shunt wire runs parallel. One end of the shunt wire connects close to the battery and the other end of the shunt connects closer to where the alternator tees-in.

The shunt wire goes through the ammeter. Since this wire is small, it only carries a fraction of the current. Much safer than sending a large 8-gage wire carrying a full 60 amps into the cab through the ammeter.

When the battery is low and being charged by the alternator, current travels one way through the ammeter and the needle shows a C value. If the battery is fully charged and the alternator is basically supplying power to all the accessories, no current travels through the shunt and the needle remains centered. If there is too much demand for the alternator to keep up or the engine is off and the battery must supply power to the accessories, current travels the opposite direction in the shunt through the ammeter and a D value is shown. Somehow the regulator is part of this circut system and things get really confusing.

Having the wires swapped at the ammeter will show a Discharge then the battery is actually charging and vise-versa. When you flip your headlights on when the engine is off and the needle goes toward D, you have it correct.

 

Hi Like M. The shunt is the heavy wire, it's shunting the majority of the current. Here's a '68 diagram for the ammeter. The gauge has two wires, 655 (red) and 654 (yellow). They both go through connector "B" and "D" before they split off. After connector "D" the red wire (now 655A) goes thru a 4-amp fuse and connects to the battery side of the starter solenoid. The yellow wire goes thru connector "C" (now 654A) and thru a 4-amp fuse. Then it is spliced to wire 38 (black) that connects to the alt (the black dot). The black wire from the splice to the solenoid (38A) is the fuse link and also acts as the shunt for the ammeter.

 

Barry, it looks like your diagram is possibly more accurate than what I was looking at before; but I am having a hard time reading it--could you e-mail me what you have there. There is something about FTE gallery images that really get distorted. I might be adding an aftermarket ammeter and I would like to know all I can about them.

Here is what I was looking at before, it it from my Ford 1969 Truck Shop Manual. It doesn't really describe exactily what the shunt wire is, I just assumed it was the one that passed through the meter and took only a fraction of the current.

 

You guys are the best! Could one of you email that diagram to me as well? The Painless directions tell me how to wire it either way. I guess I'm still wondering which post would be considered the positive and which is the negative. Electrical is my biggest weak point.

 

Forget the original ammeter. I have owned dozens of these trucks including 2 new ones in 74 and 76. I have yet to see the needle move on an original ampmeter. Install a volt meter as they will give you a lot better idea of what is going on with your whole system.

 

I second that motion.

 

willowbilly, are there replacement volt meters that will work in the original cluster?

 

Sorry I didn't respond sooner, I've been gone over christmas. I am not aware of a voltmeter that fits in the original cluster. I am currently pieceing together a F-600 insterment cluster for my 68 and plan to use a volt meter in it.