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Originally Posted by VetteVet
4. Now her is a big difference between the two. All the positive power to your truck goes through the amp meter and there should be two large wires running to it. The fourth diagram shows how it is wired. I think the 63 was the last year this style amp meter was used. The 64 diagram shows a charging light in the diagram I posted. It looks like the amp meter in your attachment has the red and black wires going to it.
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I haven't been able to pin down the exact year GM changed from the full flow to the external shunt type ammeters. However, some of the wiring diagrams in the 60-66 truck assembly manual seem to indicate that it may have been as early as 1960 (at least for some models/applications). And it appears as though the C/K series were pretty much all changed over to the external shunt type by 1961.
From what I've seen on the 1962 wiring diagrams:
The cluster harness is considerably different. But you've addressed that issue already by replacing it with the correct one for gauges.
The dash harness is basically the same for trucks with either warning lights or gauges. GM simply re-used the dark green "hot" light wire for the temp gauge. And they re-used the red "gen" light wire for one leg of the ammeter circuit. They also re-used the light green "cold" light wire for the other leg of the ammeter circuit. Yes, that does make for inconsistent color coding having that leg of the circuit change between black & light green.
The engine harness is slightly different for warning lights vs. gauges. The light green wire for the "cold" light is not present in the gauge style harness. Instead, there is a black wire with a 3 amp inline fuse that connects one leg of the ammeter to the "BATT" stud on the starter solenoid. To duplicate this (minus the color code) you could simply disconnect that light green wire from the old temp switch, add an inline 3 or 4 amp fuse, and connect it to the starter solenoid "BATT" stud.
The front light / generator harness is the same for trucks with either warning lights or gauges. However, there is a very important connection difference at the voltage regulator. Trucks with warning lights have a 20ga red wire for the "gen" light connected to the "ARM" terminal of the regulator. With gauges, that wire gets moved over to the "BATT" terminal on the voltage regulator. The 1961 Chevy truck shop manual supplement has the following to say about that connection:
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When the vehicle is equipped with an ammeter, it is absolutely necessary that the 20 gauge red wire be connected to the BATT terminal on the voltage regulator. If the wire were connected to the ARM terminal of the regulator, a dead short would result which would quickly burn up the wiring in the ammeter circuit. To guard against this occurring, a 3 amp fuse is included in the ammeter circuit. This fuse is located in the wiring harness just ahead of the dash connector on the engine side of the dash panel.
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I'd also recommend adding another 3 or 4 amp fuse inline with that 20ga red wire. That'll give you a fuse in both legs of the ammeter circuit to protect against over-current through the meter and shorts to ground on either leg.