Join Date: Sep 2000
Location: Shrewsbury, MA, USA
Re: Console AMP Gauge with one wire Alternator
Some of you guys have a gross misconception of alternators, ammeters and electricity. Stock alternators were rated at 31, 37 or 63 amp outputs and were perfectly adequate for all the electrical loads in these old cars and could still charge the battery at the same time. The charge wire from the alternator went to the horn relay terminal which acts as a distribution point for all the electrical current needed by the car. The alternator is connected to the horn relay with a length of 10 gauge wire. That wire is rated at 30Ato 50A depending on the wires temperature ratting and insulation type. A normal 90 degree C rated THHN cable is rated at 30A. The 12 gauge charge wire from the horn relay terminal to the battery is rated at 20A. Putting a 160A alternator in the car and connecting it straight to the battery positive terminal will severely overload that charge wire assuming you had a need to all that current somewhere else in the car (huge stereo system, electric fans hydraulic suspension system, etc) and your asking for a fire in your wiring harness. All of that junk needs to have their own positive power cables run straight off the battery terminal, with their own fuses sized to protect the size of the wire you use to connect the loads to the battery.
That 6 foot length of no. 12 gauge charge wire is the shunt for the ammeter so if you increase its size to carry more current you lower the resistance of the shunt and the gauge becomes less sensitive (effectively the scale of the ammeter increases). The ammeter in these cars is only meant to monitor the current flowing to and from the battery over that charge wire, it does not monitor the output of the alternator, as that is immaterial to the operation of the car. If the battery is charging there is enough current being produced by the alternator and that's all the gauges are meant to do. Be aware of what you are doing when you add large electrical loads to these older cars (or any car) as the wiring systems were never designed to carry any continuous current loads higher than about 15 amps on any one circuit, and no more than 30 over all of the circuits. If you have a need for 160A of current, I'm hoping you made significant wiring modifications to support that load.
1969 Indy Pace Car
350/300HP RPO Z11
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