I need some help asap. my alternator puked out and we installed a new one. the alternator light was out for a few minutes after the new alternator was put in, but after a couple minutes, that light was bright as day. We took the alternator out and had it tested, and it showed that it was putting out a charge. We checked the wiring to make sure that it was right, and it all coincided with how the old one was wired. We checked to see if maybe it was just the light by disconnecting the battery, but as soon as the positive came off, the truck died. We are at a loss. Any info guys? If it helps any, the truck is a 78 F-150, the engine is a 73 429 out of a Grand Marquis. Thanks!!

Mike

 

First off, welcome to FTE.
Second, it's never a good idea to disconnect the battery to check the alternator * With the Engine Running*.
The voltage spikes that occur can blow electronics, including the alternator or regulator. Another thing that happens a lot is putting a new alternator in with a dead or nearly dead battery.
It overloads the alternator and can burn it out.

Do you have a voltmeter?
Have you checked the regulator and the fusible link between the alternator and the starter solenoid?

Post back with more info and I'm sure someone here can help.
Hope this helps.
Greg

 

Thanks for the welcome Greg. ANd yes, we checked the link and put a new regulator in this afternoon. that light is still bright as day! I swear, the electrical gremlins took over my truck....lol
As for the battery, we had it running for about 20 minutes to give it a little juice, so I dont know if that is enough to do it. But it has no problem cranking over, but the one thing we did notice, and I dont know if it has anythign to do with the charging system, is that it runs at a super low idle, maybe running at 400 RPMs, I mean you can almost hear it hit every lobe it is running so low. Any other advice? thanks.
mike

 

Check the ground from the engine to the chassis. If you can get some voltage readings at the battery terminal on the alternator and on the field terminal. Also, if you have the slip-on connections for the field and stator wires, make sure they didn't get stretched out creating a bad connection. Or reversed.
Just some thoughts.
Greg

 

Check the connector to the regulator as they tend to corode on the contacts. Also will the light go out if you rev it up a little?