Old Dodge van electrical question?

So, 1994 Dodge Ram Van.  77500 miles.  Mostly original.  Runs fine.

Ammeter in dash reads low.  The extremes are labeled 18 and 8.  It runs at like the first unlabeled mark above 8, which causes me some concern.  Seems like it ought to be higher.

Voltmeter on battery terminals with engine running reads like 12.9.  Battery at rest around 12.3.  Battery is between 3 and 4 years old.

Change battery?  Change alternator?  Change both?  Something else? 

Is the voltage regulator internal? Computer controlled?

Either way, you should be in the 13.5V range. Sounds like alternator to me. Is an armature shop anywhere around?

In reply to wheelsmithy (Joe-with-an-L) :

No, and unfortunately, my son is planning a trip of some duration on Tuesday, so whatever gets done to it will get done tomorrow.  Pretty sure I can get a 120-amp alternator and a battery that quickly.

That's a volt meter, not an ammeter.

If the needle sits in a spot key on engine off, then it is higher engine running, that means it's working.

If your testing voltmeter is accurate, and only goes 12.3 to 12.8, that's a problem.  Is that at idle, with a fully charged battery?  Try around 2500rpm and see what happens.

Voltage regulator is in the ECU.   They do fail.

I bypassed the internal VR in my 1990 DogeVan with an external voltage regulator, but it will cause you to trip your Check Engine light.

Streetwiseguy said:

That's a volt meter, not an ammeter.

Oy!

You are most definitely correct!

Streetwiseguy said

If your testing voltmeter is accurate, and only goes 12.3 to 12.8, that's a problem.  Is that at idle, with a fully charged battery?  Try around 2500rpm and see what happens.

Raising engine speed produced only a small increase in voltage.  From 12.8 up to 12.9.

Battery took a 4-hour drive today, so it ought to be fully charged, or as charged as this alternator can charge it.

Sounds like the alternator or regulator is toast.

At full tilt, the alternator should be capable of over 14v.  14.7v is kind of the industry standard for bulk charging a car battery.

Well, I got a 120-amp rebuild from O'Reillys this morning, with a "Lifetime Warranty".  Son wants me to wait until he gets back home so he can help put it on.  I sure hope that does the trick.