What alternator should I get for my 1979 Silverado?

yellowdog5

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1979 Silverado I need an alternator don't know what to get. It has just basic stuff like lights, heater, wipers radio etc. I do pull a stock trailer sometimes. Can I tell which one is on it now? It's probably the original one.
 

crpntr78

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I should think the parts store people will tell you which one will work for you with the year, make, and model.
 

Turbo4whl

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Back in 1974 when the 10SI alternator was still a relatively new entity, my '74 Jimmy came stock with a 37 amp alt. With more electrical options you would get a 61 or 63 amp alt.

Now, aftermarket wants to cross fit more vehicles, you will not find the lower amp alt. You can buy one even higher than 63 amp, but like you said, you don't need it.
 

SirRobyn0

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I would second the don't need a really high amp alternator. I have seen guys jump up to the 100 + amp alternators and then have trouble with the belt slipping if they run the battery down because of the load. Best to stick with something reasonable like the 63 amp
 

75gmck25

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You can use a stock 63 amp 10si ( highest amps when your truck was built), or a simple upgrade is a 94 amp 12si with a v belt pulley. I used rebuilt 12si on my ‘75, and also upgraded the alternator charge wire with one I pulled from a newer GM truck.

if you think you want a 12si I can get the Lester number from the one I bought. Lester numbers are a standard reference for alternators , so you can find the right match without knowing the specific vehicle it came from.

Bruce
 

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@yellowdog5,

Yeah, I had a 55 amp originally on my '74 and I always rebuilt my own alt., bearings, diodes, voltage reg., etc., and all if it needed it. But I decided to buy a new one this time to kind of start from scratch. But you can't get a low amp. alt. anymore., even like my 55 amp. one. The lowest number is like @75gmck25 says, is 63 amp. one. Since you don't have computer anything, electric fuel pumps and such that comes on new trucks these days all you need is the 63 amp. one. Now, if you ever do swap out for a LS engine, like is popular these days, then you will have to upgrade to the higher amperage alt. because then you will have all the extra electrical needs of modern engines.

And also you probably have a three wire alt. like my '74. There are a lot of "one wire" conversion kits these days you might look into.
 

Matt69olds

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As long as you upgrade the heavy gauge wire from the charge stud to the battery, there is no downside to having a high output alternator.

A alternator for a sane year car, with the same engine, with power windows/ electric rear window defog will be a easy bolt on, minus the wire upgrade.

A mid 80s Camaro with a sbc will have a 78 or 94 amp alternator, which will be plenty
 

SirRobyn0

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As long as you upgrade the heavy gauge wire from the charge stud to the battery, there is no downside to having a high output alternator.

A alternator for a sane year car, with the same engine, with power windows/ electric rear window defog will be a easy bolt on, minus the wire upgrade.

A mid 80s Camaro with a sbc will have a 78 or 94 amp alternator, which will be plenty

Since you brought that up. I'd like your take on this scenario. So a lot of these trucks rolled with a 63 amp alternator and for years it was common to get those as replacements. Now it seems like the 63 is only common on remans. Going new 78 and 94 seem to be the most common. AC Delco still makes a reman 63 & 78 but only new is 94. This is as listed for the square body trucks in 1984 by application at least at a local wholesale outfit near the shop. So my question to you, I don't see an issue jumping from 63 to 78, but do you think a wiring up grade is in order for a 94amp? Assuming the truck doesn't have a bunch of additional electrical add ons. My thought has always been that the alternator won't charge that hard for that long even on a very low battery to need wiring up grade. On the other hand if something like an electric fan is present then yes it would be needed.
 

Matt69olds

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I’m guessing a 63 amp alternator would have a 10 gauge alternator output wire. If you installed a 78 amp, I’m guess you would probably be ok. Jumping up to a 94 amp would definitely have some problems. With the alternator at maximum output, the battery might get 65-70 amps of current, the other 20-25 amps would be heating up the charge wire until meltdown. if you install an alternator with more than 78 amps, definitely upgrade to a 8 gauge wire.
 

75gmck25

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I replaced my alternator several years ago with a 94 amp 12si and its still going strong - doesn't mean its the best solution, but it has been reliable.

- Take a look at the alternator picture, which shows its Lester number 7294-3, which is for a 94 amp, 12si, with terminal position at 3 o'clock. You can cross reference this to Delco parts numbers or other brands and get a similar alternator. It is a direct 3 wire bolt-in to your current 10SI.

- The other picture is my (messy) routing of the charge wire. I used a charge wire from a 90's truck (8 gauge, with fusible link) and ran it from the alternator BAT terminal over to a junction on the fender. From that junction I ran another short 8 gauge wire to the battery positive.

- I use the same junction to connect my high amp headlight wiring and a connector for a battery trickle charger.

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