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Old 08-13-2020, 11:01 PM   #26
tdangle
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Re: Stock alternator to 12 SI alternator

Few months old thread, but exactly what I'm going to do shortly. Should the 12R wire be upgraded to a bigger gauge. I assume 12R stands for 12 gauge, Red. Is there anything special about the wiring to make the amp meter work? Per info I found it looks like 12 gauge will flow 41 amps. Enough for a stock 37 amp alternator.
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Old 08-14-2020, 08:49 AM   #27
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Re: Stock alternator to 12 SI alternator

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Originally Posted by tdangle View Post
Few months old thread, but exactly what I'm going to do shortly. Should the 12R wire be upgraded to a bigger gauge. I assume 12R stands for 12 gauge, Red. Is there anything special about the wiring to make the amp meter work? Per info I found it looks like 12 gauge will flow 41 amps. Enough for a stock 37 amp alternator.
Here'e a page that explains how to wire the amp gauge (and volt gauge).

http://6066gmcguy.com/ammeter.html

As for the 12 gauge wire, I think that should be fine, but I'm no expert. I used 10 gauge, I wanted to err on the side of caution in case I add electric fans.
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Old 08-14-2020, 07:38 PM   #28
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Re: Stock alternator to 12 SI alternator

It depends on what you mean by "the amp gauge". That site does not show how to wire the stock amp gauge from a 67-72 Chevy/GMC truck. It covers how to wire an amp gauge that has a built-in shunt, so that would be an aftermarket or some other model year or make amp gauge. The stock amp gauge for 67-72 uses an external shunt. The shunt is the 12 gauge red wire that runs between the battery and alternator, and in order for that to show all charging and discharging of the battery, no accessories are connected at the battery or starter.
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Old 08-14-2020, 08:48 PM   #29
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Re: Stock alternator to 12 SI alternator

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It depends on what you mean by "the amp gauge". That site does not show how to wire the stock amp gauge from a 67-72 Chevy/GMC truck. It covers how to wire an amp gauge that has a built-in shunt, so that would be an aftermarket or some other model year or make amp gauge. The stock amp gauge for 67-72 uses an external shunt. The shunt is the 12 gauge red wire that runs between the battery and alternator, and in order for that to show all charging and discharging of the battery, no accessories are connected at the battery or starter.
Oops, thanks for clarifying that. I found that site a while ago and bookmarked it for when I wanted to tackle getting my gauges straightened out.
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Old 08-14-2020, 11:25 PM   #30
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Re: Stock alternator to 12 SI alternator

I'm looking at a 100 amp alternator. If I read the charts I've found correctly, I should probably have a 6-8 gauge wire off of the alternator
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Old 08-15-2020, 12:00 AM   #31
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Re: Stock alternator to 12 SI alternator

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I'm looking at a 100 amp alternator. If I read the charts I've found correctly, I should probably have a 6-8 gauge wire off of the alternator
The question is, where does that wire run to? If you have a load that will be drawing a bunch of current, you can run it to that load. If you expect the battery to supply a bunch of current to a device when the alternator is not running, then I suppose the wire from the battery to the alternator and that device also needs to be fat.

I don't have any big loads to worry about although I have a big modern alternator, so I didn't do anything to the stock wiring. I suppose it will be a good idea for me to add a fusible link at the alternator to reduce the risk of the alternator cooking my 12 gauge wiring if I have a short.

If I were to add something that hogs a lot of electric current, I think I would power it from the alternator with a fat wire and use a relay to only connect that device when the alternator was running. The CS144 alternator I have supposedly has a tach output that I would send to a driver/computer for a relay. I can't think of any big current draw that I want to add. Electric fan doesn't make much sense since the engine is right there and works with a mechanical fan far better than converting rotational power from the engine to electricity and then converting that electricity back into rotating a fan. That would be very inefficient to do that energy conversion twice. Electric fans are for front wheel drive cars when the engine sits in the engine compartment sideways. Just my rambling opinion.
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