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Old 05-22-2012, 01:59 PM   #2
VetteVet
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Join Date: Jan 2005
Location: Kalamazoo, Michigan
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Re: 65 C10 alternator conversion w/external shunt ammeter?

The first thing you need to do is get it out of your mind that the ammeter provides the resistance for the alternator to charge. It has nothing to do with whether the alternator charges or not. All it does is read the voltage differential between the voltage at the battery and the voltage at the junction of the alternator feed wire at the end of the shunt wire.

The resistance for the alternator for terminal 1 comes from either the charge light via the brown wire inside the cab to the firewall block, or the resistance wire from the key switch to the same place inside the cab on the firewall block. This is a brown wire with a white stripe and can be clearly seen in the diagram below. Of course you can always wire in a resistor if you don't have either of these options.

Here is the diagram inside the cab and you can see each of the two wires and where they terminate on the firewall block. Look at the ignition switch in the top center of the diagram and the brown/white wire is on the top of the switch. The charging light wire is on the right side of the diagram and it has a tan wire that comes from the light to the same place as the brown/white wire.

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Here is the engine side of the firewall block showing the brown wire going to the external voltage regulator and the jumpers for the conversion.

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The ammeter will still work with the three wire alternator as long as it is wired correctly and the inline fuses are good. There are two wires that go to the ammeter from the charging circuit. One is a black wire that runs from the terminal junction on the passenger fender on the 67 to 72 trucks and I think on the older ones as well.

It will share the junction with the battery positive fusible link wire and the battery end of the shunt. The fuse is a four amp and is in a little football shaped holder. They are sometimes hard to find. The other wire is a black with white stripe and joins the alternator junction with the alternator end of the shunt wire and the wire that feeds the cab circuits.
These two wires run to the firewall connector and then to the dash plug. The shunt and the fuses are in this one.

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