Alternator test procedure

[Jarlaxle]

I used to know this, but it's been a while, and I really don't want to smoke anything if I forgot. I'm 98% sure my (new ) alternator is bad. Voltmeter was not steady (acting like a bad diode), and it died completely Friday. I know there's a procedure to see if it's actually the regulator, but I forget what it is.

Also, to be sure: I recall that 70 to at least the late 80s alternators-Chrysler squareback or the later Densos-are plug and play, right? Because at this point, I trust one from a junkyard more than one from Auto Zone.

 

[Darter6]

If you have a dual field unplug 1wire connector and ground the terminal to the alternator case.
Doesn't matter which field wire.
This by passes the regulator giving full voltage.
I believe Square back are rated at 74 amps and yes mid-late 70's 80's.

 

[Inertia]

Turn the key on, don't start
Pass a piece of ferrous metal in front of alt, - if magnetism strongly sucks the metal to the alternator pulley, the regulator is working.
So is the rotor, brushes, field wire connections.
If it's not putting out decent voltage, (should be 13.8 to 14.2 vdc)
Problem is likely rectifier. ( Diode )
If no magnetism, regulator, brushes, wiring/connections likely the issue.

 

[Jarlaxle]

It's not putting out ANY voltage (12-12.5 running), but the voltage jumping before it failed makes me think diodes. I'll check tomorrow, now I'm off to work.

 

[AJ/FormS]

And don't forget, Mopar alternators have brushes ........ which sometimes stick in the not-touching position.

 

[Jarlaxle]

Alternator is fine. Which means all THREE regulators I tried are bad.

Any good ones left, before I set the car on fire?

 

[67Dart273]

Don't discount the REST of it. I have found OPENS in the CHARGE WIRE/ ammeter circuit. In other words, the alternator / regulator were just fine, but the power could not get to the battery. Monitor voltage AT THE alternator stud. If it is way way high, but not charging, you have a problem in the charge wire

It's VERY helpful to actually know kinda how these work

FIRST, the VR MUST BE grounded. MUST

The 70/ later has a power wire from the "run" circuit to one of the two alternator field connections. (light blue.) This also branches off and feeds the VR. The green wire from the VR sort of controls the "amount of ground" at the alternator to control it's output. More field current, more output.

Don't discount being fooled. If you remove the green and ground that field terminal, how do you know the blue is supplying power to the field? CHECK it

 

[67Dart273]

If you have a dual field unplug 1wire connector and ground the terminal to the alternator case.
Doesn't matter which field wire.
This by passes the regulator giving full voltage.
I believe Square back are rated at 74 amps and yes mid-late 70's 80's.

Sorry this is NOT TRUE

If you are going to ground one, it MUST be the GREEN wire that you disconnect. The light blue is switched 12V TO THE field, and by disconnecting and grounding the opposite field terminal (the one where the green was) you are causing full power through the field. If you remove the blue, and then ground that field terminal, you are grounding "nothing."

 

[Jarlaxle]

Alternator tested fine. The wiring MUST be good, because it worked fine for several months.