Sorry if it's hard to read some parts, my first language is not english.

I got a 87 Camaro a couple of weeks ago, the engine was swapped from a v6 to a 350 so i'm told by the previous owner (he is not the one who swapped it and hasn't have much info)

From what I know its a 350 from a 79 corvette but we are both unsure. There are many small things i need to address since this swap is half hacked, but my primary concern at the moment is the charging portion.
From what I've been able to see the alternator on the car at the moment is rated 78A, so not sure if that is an issue by itself or not as it seems low to me.
What i can read on it (although its pretty hard to see the stamping) Delco 1105 521 Y 78A 026 12V NE6 but this doesn't seem to give me anything of value on google.

When I start the car the voltage stays at around 12-12.5v, worst if i put lights on etc. but battery never dies so I'm guessing it's charging at that voltage
Nothing changes when I rev the car, SOMETIMES if I rev it will start charging "normally" and stay there unless if i put lights on etc then it will dip to around 13ish.
This doesn't always work, and sometimes without revving it will start to charge as normal at some point while driving, but this isn't always the case.
Also this alternator only has a 2 wire plug and it should more from the research i've done.

one of the wires go to the battery post on the alternator and the other goes through the firewall near the rear of the engine block (thinking it goes to the voltage meter in the cluster) and this wire sometimes i get 0v and sometimes about 8v
The fan fuse is good, and i have no fan relays near the driver firewall or near the battery (i have a clutch fan on the engine)

There should be an exciter wire to tell the alternator to charge from research , so im guessing its the wire which i get 0v or 8v from (im pretty sure when its at 8v i get the alternator to charge, i need to confirm this not at the car atm)
Sorry im at a lost here, no idea what engine i got, or what alternator is installed + hack job makes it hard for me to know where to start/look at.
Any help is appreciated here.

 

So on my way home, the alternator was charging at about 13.5v and was getting 8.3v at the wire from the firewall.

No idea if its connected or not but usually the temp and oil pressure dont work in the dash, but where working in this instance.

Also rpm and speedo have never have the right readings(both wayyy to high)

Maybe the issue is with the cluster?

 

The alternator is a model 12 si of 78a and was commonly installed on 1983-86 carb v8 3rd gens and other GM cars. 78 amps is plenty,especially with an engine driven fan. Alternator could be faulty,but iffy wiring will need sorted first-if there is remains of 1987 v6 port injection wiring left could see if the original alternator exciter wire is the one hooked up-original alternator on an 87 is a cs130 with a 4-pin alternator plug,probably only using 2 of the pins.

 

Is there a way to know exactly what engine the car had factory so I'm able to pull out the wiring diagrams? VIN ? and where would I go to check this.
Thanks for the help

Edit:
With the VIN, was able to figure out the engine was a 350 from factory.. 1G1FP2182HN169112
So the V6 theory is out the window, don't understand why they hacked in a 83-86 alternator instead of just putting the same thing back in plug and play.

 

If car came with 350 from factory,it was an IROC Hard to say why the earlier alternator was used-could be replacement engine had that alternator on it-alternator has 1985 date code,but who knows if original to engine.1987 350TPI would use a cs130 alternator mounted the same as that 12si.

 

So I have changed the alternator for a ACDelco 335-1005 (with ACDelco Gold PT2297 connector)
I have installed the wire from the output to the battery with a fusible link. There is a ground wire to the battery on the lower mounting bracket
I am still having trouble finding the problem of my brown excite wire from the car which sometimes gives 8v (thinking this should be 12v?) and sometimes nothing, so i decided to bypass completely with a 12v ignition source for now (used power from the Fan fuse under the dash since this isn't used anymore in my setup) I have a 20A fuse on that bypass wire (no idea if it's too high or not but I just reused what was there for now)
from what i read i only need one wire to make the alternator charge on either the L or F pin and S pin wasn't needed.
I don't have the S pin wired to anything (this should go to the positive on the battery but i didn't have thick enough gauge wire and since i saw that this wasn't needed I passed on it for now.
Now if i connect to either the L or F pin, the alternator charges at over 14v BUT I'm getting a pretty noticeable whining sound from the alternator itself. If i remove the 12v ignition the alternator doesn't whine at all. both Land F have the same results.

But as a plus, now my voltage doesn't go down if I put on all accessories/lights on. At least now I know the old alternator wasn't strong enough or was dying.

Now my questions;
- is it true I only need L or F to excite the alternator and nothing on S
- Does having nothing on the S do anything? If i install a wire, what gauge and what size fusible link do I need?
- for the whining, would it be a bad alternator? something else? I do not have a resistor on hand at the moment for the excite, would this cause the whine? It seems to completely disappear if i rev. or if no excite source is wired
- Do I absolutely need to have a resistance on the excite wire ? Again I see conflicting information on this.

Thanks

 

Add a ground wire from the block to the chassis. I had to do that after I had the alt rebuilt & rebuilder painted at same time. The painting broke the grounding of the alt to the block.
After rebuild, the alt would get very hot & stop charging when the headlights were on. The ground wire solved the problem.