Bad Alternator? '74 targa
 

How do I distinguish between a bad battery and a charging problem?

I think I am getting old as at the end of last summer I bought a new battery but was convinced I really had a charging problem.

I starter her up today for the first time since October and the red "g" light came on as usual at low rev's and warm up - I went for a 20 minute shake-down and all seems to be normal - that is my "g" light was on at low rev but went out under normal driving.

I'd like to take a 50 mile drive tomorrow but I am scared I have a bad alternator - whats the test?

Felt soooo good to have the car out again - I even loved smelling like gas and exhaust all day ; ).

Buy a digital voltmeter that plugs it into the lighter socket. Watch to see the alternator is working and putting out around 13.2 to 14 volts depending on the charge state of the battery.
If it is jumping up and down all over the place, your regulator may be on it's way out, or your alternator is.

End of last summer? As in 9 months ago? Charge it. Bad batteries happen all the time. Charge it out of the car to full (overnight) on a trickle charger and put it in. It probably is a bad battery - batteries should be looked at first as they are usually suspect - it baffles me how many people look farther down the line from the battery, assume it's not the battery, or if it's a new battery assume that it's good. Batteries are usually the culprit.

awesome thanks!

I was assuming a fully charged battery...
Make sure it is!

12.5 minimum volts on the battery. 13+ at idle
13.5 -14 at 2500 rpms.

You may need to install a resistor in across the warning light bulb terminals to keep it charging at low rev's.