alternator wont charge

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oley340

oley340

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i have a 70 340 duster that stopped charging. we rebuilt the alt replaced the voltage reg and ran all new wires from the volt reg to the alt. i have 12v coming in and still no charge does anybody have any idea's not sure were to go next. Thanks for your help
 
Single or dual field alt? What are you using to tell you it is not charging? Volt meter or the factory amp gauge. The voltage regulator needs a good ground, as does the alt. Is there a good ground from the engine to the firewall? I usually run a dedicated ground from VR to the Alt.
 
Did this problem crop up before or after all this work?

Divide the problem into

1--Charge/ output wiring
2...Field wireing
3...the alternator itself
4...the regulator

in no particular order

Start by disconnecting the field wire which runs back to the alternator. This was originally GREEN. Ground that alternator field terminal with a clip lead, start and run, see if it charges

If not, measure field voltage at the remaining terminal, with key on/ engine off. Should be same as battery. Disconnect and reconnect your ground clip. In subdued lighting you should see a small spark.

With the engine running measure battery voltage and then alternator output stud voltage.

if they are the same, and below 13 with engine running "fast" then not charging. If voltage at alternator is quite high but battery low, then you have a wiring problem in the output circuit

If voltage is climbing up at battery, it is charging and problem is elsewhere
 
If the test above shows a charge, reconnect field wire, move up the regulator. Disconnect the connector and devise a method of jumpering across the VR harness connector. Two small machine screwss will work. Now move to the alternator, and disconnect the BLUE field wire, and ground that field terminal. Again see if it charges

If it charged earlier but not now, you have a wiring problem in the VR field circuit. If it does charge.......

Make CERTAIN the VR is grounded. Scrape around the mounting holes and mount tight with star lock washers. "Work" the VR connector in/ out several times, and examine it closely for looseness/ corrosion. If no charge, replace the VR
 
I wont type the entire story of my neighbors recent alternator fiasco. The first reman'd alternator he got from Advance did not work. He spent that Saturday night in his Silverado. On Sunday morn' he took the alternator back and got a second ( had to switch the pulley this time ). It worked fine.
 
^^Good point Redfish. READ!!!! There has been a NUMBER of "rebuilt" alternators show up right on this board with (incorrect) grounded field terminals or isolated field units (incorrectly called "dual field") being sold for older 69/ earlier applications

CHECK YOUR NEW ALTERNATOR!!! Check continuity to the case with both field terminals. Should be OPEN, or INFINITY

Check field--to--field terminal....Should be a very low resistance.

This is for 70/ later with TWO field terminals
 
Thank you I will try your ideas this weekend grounding seems to be the problem
 
All that 67Dart273 said. I'll add that once a new alternator didn't show charging on the dash ammeter after a quick swap in the auto parts parking lot. I was about to take it off and return when I got the bright idea to clip a jumper cable from the alternator's case to BATT-. That was the problem. The engine was grounded fine, but there was corrosion at the bracket mount, so the alternator case wasn't getting grounded well. That is the return path for the alternator's output current. I reinstalled the old alternator and it also worked w/ the jumper, so I did return the new one. A little sanding at the bracket contact fixed it. That was a slant six, w/ standard 1-field wire alternator (30A ?). Not sure what inspired trying that since I was fairly newbie w/ cars then.
 
gonna look at grounding this weekend. It must be something simple it was charging fine and i have checked and replaced everything.
 
A couple of years ago, there were a bunch of bad regulators out there. BWD brand (standard motor products), carried by Advance auto parts. The internals were not connected to the case, so there was no ground, What pissed me off was Standard knew about the problem, and did not recall them.
 
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