Ive been messing with this charging issue for a few days now and I'm stumped I really need some help.

I'm only getting a max of 10volts at the back of the alternator at all times I've tried three didferent ones including one off my brothers iroc which works perfectly on his car.

I have the brown wire going to G8 on the c100 hooked up it has power on key on
The red fat wire on the plug is connected to the back of the alternator

From what I understand it should be working corrctly the way its wired I check for draws in the system and everything checks out i'm only powering a holley blue external pump and an electric water pump I've ran the car with both of them disconnected and it makes no difference
can anyone help I don't know anything else I can try to get atleast 12v out of the alternator

 

You need to check a couple other things. I assume you have 12 volts or battery voltage on the brown wire on the plug for the alternator which is correct. There is also a red wire in the same connector for the alternator which should have 12 volts or battery voltage also. The big wire thats bolted on the back of the alternator should be 12 volts too. Need to check those wires. Here's a diagram to help you out.

 

With a frshly charged battery it will show 12ish volts but as soon as the car starts they will keep dropping and dropping
I went off that specific diagram to wire and check everything austinthirdgen has some very detailed diagrams I check all those already I'm getting 10v on everything.

I thought there must be a draw somewhere so I ran it with both the water and fuel pump unplugged and the volts go up more to around 10.7v but still not enough volts eventually keep getting lower and lower

I'm assuming it may be the way I have it wired but all the searches I've done lead me to believe everything is good but still won't charge

 

I also tried different key on power sources for the brown wire going to the plug And no difference

Here's what the set up currently looks like

 

Bump

 

You probably have the wrong alternator for the car since it looks like its not the stock one. What year and vehicle did the alternator come off of? The diagram is for the stock alternator which looks like you dont have anymore.

 

That is an oe style alternator the car is a 1991 RS
I just pust a v belt pulley on it and made a bracket to mount it

 

Only thing I haven't tried is a new plug
I'm gonna do that next

 

Only thing I can think of is your losing battery at the alternator to make it charge. Try testing for power at the connector with the connector plugged in. If your testing it with it unplugged, you will show battery voltage but try keeping it plugged in and back probe the connector a see if your getting battery voltage with the engine running. You might be losing voltage when you put a load on the wire or wires.

 

Very good point
I'm gonna throw on a new plug tomorrow
before I heat shrink and soder the connections ill test it with it plugged in and see what going on

I appreciate the help

 

So i put a new connector and took the alternator off my brothers Iroc and put it on mine because i know it works. I put 12v key on thru a relay to both the Red and Brown wire on the plug the power source to the relay was coming straight from the battery.

It still will not charge

I did modify my engine harness
power distribution is still at the starter

I have isolated the alternator from any possible draws in the system so if the harness was bad it would work when its isolated from everything and the brown and red wire are getting 12v power right?

I even went as far as putting a ground strap to the alternator from the frame and it did nothing different still wont charge.

 

i found a picture of how i had it wired before and it didnt charge that way either

 

I went and looked at my iroc since its the same wiring configuration. Schmatics are the same. I see your last pic and it should be ok to have the big red wire on the connector attached to the lug on the back of the alternator. Thats where the big charge wire also hooks up to and that comes from the battery. Dont know which small wire in the alternator connector your using but on my iroc, my ignition wire is the one right next to the bigger red wire. Let me know.

 

yes on my plug its the one right next to the big red wire

there has to be something im doing wrong

i have been running this set up for a long time it worked just fine before but it was fuel injected and had all the stock wiring this time i made the harness standalone and changed to a carb set up

if i cant figure out whats wrong with it im gonna have to let it sit till i can buy a high amp 1 wire alternator

im assuming that would probably get me around all the issues with a stock OE alternator

 

Last thing I can think of is to remove the big red wire off the lug on the back of the alternator and run it straight to the battery. I wouldnt think it would make a difference but I have seen weirder things. Maybe those wires conflict with each other. They're wired separately for a reason in the diagram. Worth a try.

 

Also, did you back probe the connector with it plugged in and the engine running and see if you had battery voltage on both wires? Might be dropping the voltage with a load on the wires.

 

its not dropping voltage i put the volt meter to it again i think its the belt slipping its the last thing i can think of better i set it on fire

 

Ok, you have good voltage at the alternator and isnt dropping out with a load. I've thought about it over the past couple days and I come up with one more thing. The alternator is made for a serpentine belt and you put a v-belt pulley on it. What I thought of is maybe the alternator is spinning the wrong direction. Havent paid much attention to mine in which way mine spins, but since its a sepentine set-up, gm might spin it the other direction with a sepentine belt than with a v-belt set-up. Something to look into to. Which way is your alternator spinning? Clockwise or counter clockwise?

 

Alts work correctly spining either way. The only thing that spins backwards between the Vbelt cars and the serp cars is the waterpump. I have mounted many alts backwards for blower kits and they work just fine. Some 4.6 mod motor blowers require the alt to be backwards for clearance.

 

It spins clockwise
I've been running this set up before and it worked fine. I tore the car down and re did pretty much everything including wiring I left the charging system alone for the most part
I do have 12v at the brown wire while the car is on and hooked up to a running car with jumper wires
I've tried adding the 5 watt resistor on the exciter wire while getting 12v directly from the battery and nothing
I've tested the alternator at 2 different places and it works I must still be doing something wrong
I'm going to take a video while testing it tomorrow and ill post it maybe someone can catch what I'm doing wrong I really wanna drive this car its been down for 2 years ive replaced so much stuff on it I just wanna enjoy it already

 

So I adapted a new bracket
changed back to serpentine
Got ANOTHER new plug went back to wiring it the stock way without the 5 watt resistor
Andit works now!!
Making plenty of power even at idle to run everything
Now I can finally start driving it
Thank you Jermdm and Vetteoz for all your help