Jonk67

If the charging post from the alt. isn't fed back to the large post of the solenoid where the battery pos. connects you may not be sending a charge to the battery. Not all of the posts of the solenoid connect internally with the pos. lead constantly, it is a relay with on/off connections internally.
I have never spoken to an electrical person who advised the 'disconnect the neg. running' trick and have sold plenty of alts., wiring and VR due to this shade tree test from my previous years working a parts counter. Do it properly and have the alt. tested first to narrow the issue. In the end I'm betting it's your wiring if the alt. is still good.
Jon

jlg2002

Jonk,
I apprenticed in an electrical repair shop in the 70's and we did the take the neg cable off test all of the time. Mostly due to installing the Sun Electric VAT 28 we used to check charging systems and set voltage regulator output.
I've seen lots of condemnation of doing the cable remove test but I haven't really seen a good "technical" reason why not. I'm open to all opinions (based on fact) Anyone ?

Jonk67

Voltage spikes, same answer I got on most electrical websites, tried to find it on an SAE site but don't have time to sort through it. If the alt. wasn't bad before the test it may be after...sometimes it may fry it sometimes not but if the alt tests bad after disconnecting how would you know if the alt. was good before? I managed a parts store in the 80's and we sold many an alt. after this shade tree test, put it on the tester and the VR would be bad or windings fried, sell them an alt. The would return the same day with the part that originally caused the problem - batt. with a dead cell, batt. cable corroded internally, etc. after they put the new alt. on and didn't pull the cable they had the same original problem to solve.

http://www.bcae1.com/charging.htm

Warning!
Some people tell you that you can check your alternator by disconnecting it from the battery to see if the alternator can produce enough current to keep the engine running. BAD IDEA! Disconnecting the battery will subject the voltage regulator (and computer and audio equipment...) to significant voltage spikes which may cause an otherwise good alternator to fail. Even if there were no damaging spikes, this test would not indicate whether or not the alternator was good because the engine will easily run with a weak or failing alternator.

Simple Test:
If you want to see if your alternator is producing current, turn on your headlights when you're parked and the engine idling with the headlights shining on a wall (at night). Notice how bright they are. Then turn the engine off. The lights should get dimmer when you turn the engine off. If the lights get brighter when you kill the engine, the alternator was not charging sufficiently. When doing this test, the lights should be the only load (turn the stereo, a/c and other accessories off). With a heavy load, an otherwise good alternator may not be able to produce sufficient amounts of current at idle.

Jon

vdhillon2

I took the alternator to Pep boys after 40 minutes they told me they couldn't do the test, it wasn't working because they couldn't ground the unit due to the chrome....ummm really.
Autozone's professional employees were able to tell me that the alternator was no good based on there opinions....they too couldn't get a test result.
There is a vintage car parts store who had a replacement alternator, so i just bought another one. Tried installing it, but the belt starts to squeal and the pulley gets REALLY hot. Haven't had a chance to get back to it, hopefully this will work out. I'm gonna replace the front pulley from the original alternator. It is drilled and has aesthetic cone on it, so i'm thinking there is a size difference giving a little more tension.

Jonk67

That was going to be my guess - the pulley groove is probably a different pitch/width on the replacement. To ground the alt. all they had to do was put a spare bolt into the mounting tab with threads and then ground to the screw...there shouldn't have been any chrome in the screw hole threads, if the threads were chromed that could have been part of your issue also - poor ground.
Let us know the net result.
Jon

vdhillon2

Well that wasn't easy. The pulley on original alternator was a little larger which led to the squealing and heating up of the new alternator. I couldn't get the bolt off that thing for the life of me. After about a day of struggling with it, i finally got out the soldering torch and heat that thing up till it starting turning red, and finally it came off.
With a new alternator, and the original pulley I'm back in business.
I have 14.5v coming out of the alternator.
The battery is at 12.4 at rest. with the car started i'm getting about 13.2v at the battery.
So it looks like it was the alternator, just can't figure out why one would go out at 400 miles.
Thanks for all the help.