Car dies when I disconnect positive battery terminal

my 1970 250 ci has been dying when the battery dies. For some reason alternator is not recharging battery. Here is what I have done! I did the old disconnect of the positive cable while running and car died. I assumed it was alternator so changed out alternator. Still doing it so i had another voltage regulator laying around so I swapped it out. Still dying. My ALT idiot light is not coming on when the key is on which tells me maybe a wiring issue somewhere. I recently swapped the ignition switch because it was fried. I had a 71 switch laying around since my plastic connector was fried i matched up the wires with connectors. Is it possible i got a wire crossed in the switch that is causing this. Or is the 71 switch different than the 70. I hooked up a voltmeter to battery while running and I am getting about 12.5 volts. A buddy of mine says I should be getting about 13.5 to 14. Any ideas guys?

 

You should never disconnect the battery cable with the engine running. It causes a load dump condition that can kill the diodes in the alternator.

 

If your idiot light and resistor aren't working the alternator won't turn on.

 

Why don't you have the battery tested?

 

How do i troubleshoot the resistor and idiot light? Excuse the ignorance but what is the resistor?

 

the battery is good. I did test battery!

 

Take your car to a local auto parts store and have them test the charging system. Take the guess-work out of it. And try replacing the bulb in your ALT light. They don't last forever.

 

All one has to do to test light is ground the I terminal at regulator, if bulb and other associated circuitry are good it will come on..

http://1bad6t.com/Maverick/repair/engine_repair_02.html#c

 

Am I understanding correctly. If the bulb is not working then I would not get power to the Alternator? Does the power pass through the bulb?

 

the lighting of the bulb is what turns the alt on.

 

Wow OK thanks guys.

 

I changed the Alt bulb still does not work. Frustrated

 

In the mechanical regulator circuits the resistor is what actually excites the alt... The "bulb excites the alt" is a old myth that just won't die... If it isn't operating then likely there is a wiring problem or regulator is bad...

Do the test I mentioned in my earlier post, might just tell you something...

 

maybe on some alts...mine I had to install a bulb inline for it to charge. a friend of mine has the same setup and had to also wire in a light. it comes on with the key in the on position and goes off when cranked. on my 347 I had no light but had a switched on 12V to excite it.

 

I am not quite sure how to do this. I have located the "I" prong on the regulator. I guess I unplug it, then wrap a wire around the "I" prong and plug it back in? Then attach the other end to neg battery cable? Do I turn the key on?