Alternator wiring

[Matt69olds]

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im pretty comfortable with automotive wiring, and GM wiring in particular, I hope this is a easy issue.

GM 12SI alternators with a charge light have key on power to one side of the 194 bulb (a pink wire, usually fused on the gauges fuse) the other side of the bulb is connected to pin “2” of the alternator on a brown wire. The bulb technically isn’t required, a 35ohm resister could also be used. So how are the truck with gauges and no warning light wired? Is there a resistance wire inline with the brown charge wire? I have cut apart 2 truck harnesses, unless I’m looking right at it I’m not finding a resistance wire. What am I missing?

 

[QBuff02]

What is it that you're trying for exactly? Are you trying to rewire it a different way or just understand how it's wired? In a nutshell if I remember correctly.. It's something like it sends power both directions acting somewhat as an open circuit so the charge light doesn't light up but then when theres no power coming from one side or the other it makes the circuit act as a ground, and the light then lights up indicating a no charge state. So basically the 12volt+ from the alternator cancels out the 12volt+ from the ignition switch. That's why if you switch to a single wire alternator and cut out (or don't hook up the 2 pin connector) it still charges and works like it should because the circuit still senses charge/no charge states.

 

[Matt69olds]

I’m basically upgrading and repairing 10 years of neglect. The truck had been sitting for years, the underdash wiring was chewed up (why do mice like wire?!). I’m adding cruise, power windows/locks and delay wipers on this truck, it was pretty stripped down. I put Autometer gauges where the factory stuff went, I’m also adding small warning lamps for temp and oil pressure. Like I said, I’m pretty comfy with GM wiring, I just don’t understand how cars/trucks with no warning lamp are wired. I know with the engine running, there should be power on both sides of the warning lamp. Power on both sides, no ground, no light. If the alternator fails, the regulator supplies the ground to illuminate the light. Im also pretty sure power on the #2 terminal of the alternator is what “wakes up” the regulator. Im just curious if the resistance on the brown wire has to be there, if not, I would like to include a small LED charge warning lamp. Lots of GM cars/trucks have voltmeters with no charge light, just curious about the correct wiring

 

[Matt69olds]

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I found my answer. This is from alternator instructions for a AC Delco alternator, I’d say it would have to be accurate. I see there is no need for a resistance wire or bulb, the brown wire is a key on ignition source to “wake up” the regulator. Doesn’t matter if the power goes thru a bulb or not. Learn something every day!

 

[QBuff02]

The Brown wire is what sends signal (voltage) to the cab/instrument cluster. that should be pin#1, and pin#2 is a red wire that is hot off the starter or the junction block (I can't remember which exactly) There should be no resistance on the brown wire as it's a signal wire. In conjuction that's what wakes up the alternator. on a single wire alternator it's woke up my rpm, and some have to be revved up to like 1,200-1,500 rpm before they'll start charging. As far as no charging light goes, there's simply no charging wire circuit included, it just shows actual voltage on the gauge. I did similar to you as I started swapping in all autometer gauges when I did my engine rebuild last year. That's still a work in progress on the dash part and I had the same problem as you. My truck sat in a barn for about 4 years before I bought it and mice had wreaked havoc on most of the wiring in some way, shape, or form. little bastards!

 

[bucket]

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I found my answer. This is from alternator instructions for a AC Delco alternator, I’d say it would have to be accurate. I see there is no need for a resistance wire or bulb, the brown wire is a key on ignition source to “wake up” the regulator. Doesn’t matter if the power goes thru a bulb or not. Learn something every day!

I'm glad you found that. The same goes for the CS130 alternator upgrade. People have said for years that you need to have a resistor or bulb in the adapter harness for a truck with just gauges, but GM didn't have any type of resistor on any of the factory applications. The whole "need a resistor" thing is hogwash.

 

[Matt69olds]

I believe the CS series has a pin for a bulb, and a pin for key on power. You could use one or the other, but the pin for the bulb has to have a resistor or bulb. The “I” pin needs a key on signal. I’m guessing that’s where I got the resistance story. I have a copy of a Car Craft magazine article that explains the difference. Marlin Davis was the tech editor at the time he wrote the article, ironically his project vehicle for that article was a 69 Cutlass. Ain’t no feelin like Oldsmobiling!!

 

[Matt69olds]

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[bucket]

Hmm, I guess I don't know. I've done the swap and used a 194 bulb as a resistor just to be safe. But the first CS130 swap I did was years ago on my '86 Camaro with no bulb or resistor. It still works fine. As far as I've been able to find, as far as the ALT is concerned, an '86 and '87 Camaro harness is the same. In '87, they got the CS130.

 

[75gmck25]

Based on this article, CS130s have two versions, one designed for using an idiot light, and one that gets direct 12 volt power. https://www.hemmings.com/blog/article/delco-cs130-alternators/

The 10si/12si connections in a square body are simple.

- Run the charge wire on the threaded BAT terminal to either (1) the large post on the starter (stock setup), or (2) directly over to the battery positive post. Original charge wire should be 10 gauge with a 14 gauge fusible link. I recommend upgrading to 8 gauge with a 12 gauge fusible link. You can usually pull the larger charge wire off an 88+ GM truck and it will already have the molded fusible link.

- The other two wires run from the firewall area across the passenger side valve cover and plug into the back of the alternator.
Terminal 1 (should be marked on the case) - (excite) connects to switched ignition-on power
Terminal 2 - (sense) connects to a 12 volt always-on wire in the harness.
You can also use a jumper to connect this wire to the BAT terminal, but now you are sensing voltage right at the alternator instead of the stock connection near the fuse panel. This might cause low voltage if you have high amp accessories in the cab.

Years ago I swapped my 10si for a 93 amp 12si just to get a little more charging power. Its a direct swap for older trucks if you get a 12si with a grooved pulley and with the case clocked properly for your truck. I could get the Lester number off my alternator if you need a specific model to look for. Mine is from a mid-eighties GM car, but I don't remember which one.

Bruce

 

[bucket]

Based on this article, CS130s have two versions, one designed for using an idiot light, and one that gets direct 12 volt power. https://www.hemmings.com/blog/article/delco-cs130-alternators/

That can't be right either. I can use an '88 Celebrity as an example, as it used the CS130. When you order an alternator for it, you are not asked if it has gauges or idiot lights. A car with gauges has no charge indicator, just the gauge. I've done a cluster swap in one of mine too, from lights to gauges. It was just a matter of swapping in the correct temp sender (no oil pressure gauge) and the new gauge cluster, that was it.

My '88 Burb was the same way. When I replaced the factory CS130 alt, I was not asked if the truck had gauges or idiot lights.

 

[Matt69olds]

Well crap, I searched online for that Car Craft magazine article with no luck. I have it in my auto “library” in the garage. I’ll look for it tomorrow

 

[MikeB]

To reinforce what's been said above, here's what I learned when installing an American Autowire harness.

American Autowire says if the vehicle has a voltmeter and no warning light, the brown wire from the alternator "exciter" terminal is connected directly to the accessory bus on the fuse panel.

About a system with warning light they say: "The electrical current passing through the filament of the warning light is what energizes (or excites) a circuit in the alternator to start charging."

So, one side of the lamp is connected to the ACC bus; the other to the alternator exciter terminal. And if the lamp sees voltage on the ACC bus side, but zero volts on the alternator exciter side, it will turn on.