I have just about everything in my 3800 swap done but I have one thing that I`m not sure where to turn.
My alternator is putting out right under 16 volts.
I had it tested today and it passed.
I checked the wiring plug and the Red goes to L and the Orange goes to S.
I would assume that the PCM is somehow not telling the alternator how much to charge.
If there was a problem in the Orange wire could that cause the alternator to charge high.
Oh, I`m not relying on the gauge although it`s pretty accurate.
I have measured voltage at the battery and at the alternator output post.
Thanks

How did you measure 16 volts? If the test said it passed, then who do you believe?

I assume that when they test an alternator there is something on their machine that sends the correct signal to the L terminal
that tells the alternator to charge to an acceptable voltage.
I can only assume that if something is amiss with my PCM sending out an incorrect value to the L terminal then the alternator
could charge at a higher rate.
So, in essence I believe after testing that the alternator is capable of putting out the right charge if it is getting the right signal
from the PCM which mine could either be bad or something is wrong with the wiring to terminal L.

Oh, I measure 16 volts with a meter at the alternator post as well as the battery posts.
Even though I know they are sometimes not very accurate my gauge in the cluster is reading about
the same rate.

If I don`t get this solved in a few days I saw a video of someone using an external regulator that is fairly simple to hook up that
would be a last resort.

[This message has been edited by TXGOOD (edited 10-13-2021).]

Is the alternator new? If the test said it passed, then they probably would not mind if you exchanged the alternator for another one.....just to see if everything reads the same.

[This message has been edited by Gall757 (edited 10-13-2021).]

Alternator is one that came on the engine.

If under PCM control, Alternator wiring should be

PCM C2-61 red B or L of small plug

PCM C1-36 brown C500 B-3

BJT orange 12v from Battery Junction Terminal fused 10 amp

Have you verified these connections?

quote Originally posted by olejoedad: If under PCM control, Alternator wiring should be PCM C2-61 red B or L of small plug PCM C1-36 brown C500 B-3 BJT orange 12v from Battery Junction Terminal fused 10 amp Have you verified these connections?

Not yet. I have been trying to find out where the various wires go.
I will look at that tonight.
I read that you really only need the Red to the L terminal of the alternator.
Is this not correct?

quote Originally posted by TXGOOD: My alternator is putting out right under 16 volts. I had it tested today and it passed. I checked the wiring plug and the Red goes to L and the Orange goes to S. I would assume that the PCM is somehow not telling the alternator how much to charge. If there was a problem in the Orange wire could that cause the alternator to charge high. Oh, I`m not relying on the gauge although it`s pretty accurate. I have measured voltage at the battery and at the alternator output post.

So the "Red goes to L and the Orange goes to S?" Doesn't sound right and likely making the Alt is too high volts. Do Not run the car like that because pushing many E-parts into over volts even at 16v. (Many E-parts have only 16V Capacitors like many Radios connected to "12v" input power. While rated 16v to 20v when new... Decades later the cap ratings can degrade depending on type.)

If Red wire is bigger gauge then Orange then more likely have side plug wires wrong.

Some PCM controls the Alt. Others just monitors and plays "man in the middle" w/ battery light.
PCM controlled Alt can use F and/or P terminals as well. (See my Cave, CS Alternator)

I don't have alt wiring for that engine but many PCM controlled are this way if only two wires to side plug...
PCM Should make Alt to Turn On/Off only at best. Like the Battery Lamp did before. Using L or other pins But Not S
Alt Output and S pin should be splice together somewhere nearby in the engine harness as shown is my Cave, Alternator Sense

"Unplug" alt out and side plug. And "unplug" the PCM too. ECM/PCM may be damage/kill for next step.
Should see 0Ω on the wires to output and S terminal if wired as shown there.
If not check Alt Out and Red wire currently going to L for 0Ω.

If neither has 0Ω then need FSM, AlldataDIY, etc for the donor car to find right Alt wiring.
Example: Some PCM use Side plug P pin to see Alt RPM and could "trip a code" for belt slipping etc.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

quote Originally posted by theogre: [QUOTE]Originally posted by TXGOOD: My alternator is putting out right under 16 volts. I had it tested today and it passed. I checked the wiring plug and the Red goes to L and the Orange goes to S. I would assume that the PCM is somehow not telling the alternator how much to charge. If there was a problem in the Orange wire could that cause the alternator to charge high. Oh, I`m not relying on the gauge although it`s pretty accurate. I have measured voltage at the battery and at the alternator output post.

So the "Red goes to L and the Orange goes to S?" Doesn't sound right and likely making the Alt is too high volts. Do Not run the car like that because pushing many E-parts into over volts even at 16v. (Many E-parts have only 16V Capacitors like many Radios connected to "12v" input power. While rated 16v to 20v when new... Decades later the cap ratings can degrade depending on type.)

If Red wire is bigger gauge then Orange then more likely have side plug wires wrong.

Some PCM controls the Alt. Others just monitors and plays "man in the middle" w/ battery light.

PCM controlled Alt can use F and/or P terminals as well. (See my Cave, CS Alternator)

I don't have alt wiring for that engine but many PCM controlled are this way if only two wires to side plug...
PCM Should make Alt to Turn On/Off only at best. Like the Battery Lamp did before. Using L or other pins But Not S
Alt Output and S pin should be splice together somewhere nearby in the engine harness as shown is my Cave, Alternator Sense

"Unplug" alt out and side plug. And "unplug" the PCM too. ECM/PCM may be damage/kill for next step.
Should see 0Ω on the wires to output and S terminal if wired as shown there.
If not check Alt Out and Red wire currently going to L for 0Ω.

If neither has 0Ω then need FSM, AlldataDIY, etc for the donor car to find right Alt wiring.
Example: Some PCM use Side plug P pin to see Alt RPM and could "trip a code" for belt slipping etc.

[/QUOTE]

I`m just going by what was said in this post.
The Red and Orange wires I`m referring to are in the plug that goes in the side of the alternator.
The larger Red wire is connected to the bat post on the alternator.
https://www.fiero.nl/forum/...160323-2-123056.html

[This message has been edited by TXGOOD (edited 10-13-2021).]

I disconnected the Orange wire and now it`s charging at 14.5 volts.
So, I have one Red wire in the plug to terminal L and the larger Red wire to
the batt post on the alternator.