Proper way to test alternator

[tfbomke]

Hello all,

Novice car guy here, especially w/ electronics. But, I am very excited about my new 1971 240z and am eager to learn. Based on info from previous owner, the battery is not being re-charged by alternator due to a bad wire from alt to battery. He said he tested alternator and it was fine. My battery is charged, headlights turn on etc. Want to make sure I am doing the alt test right (The Brit slang in my Haynes manual may be throwing me off).

1. Disconnect Alt leads (From E and A terminals???)

2 W/ voltmeter put + probe on A terminal and ground Neg (ground on frame or on E terminal???) and check for battery voltage, 12 volts.

3. turn on headlights

4. start car, repeat step 2, if alt is good should read between 12 and 14 volts.

Does this sound about right? Any other tricks/tips?

Thanks in advance,

Tim

[LanceM]

2. ground on frame or battery - terminal.

That should check if the alt is working, but not really how "well" it is working. When I am in doubt about an alternator I remove it and take it to a shop that can spin it up and load check it to be sure it is putting out what it is suppose to be.

[tfbomke]

The alternator tested out, about 12.5 volts or so. For you rookies like me, the best results come from putting the Neg voltmeter probe on the neg battery terminal. The frame may have paint, rust or dirt and give a bad reading.

Now my next question. As per my last post, the previous owner thought the wire from the alternator to battery was bad and battery was not getting recharged. Does this wire run from the A terminal or the N/F terminal?

-Tim

[Arne]

Alternator needs to put out more than that - should be 13.5-14 volts. 12.5 volts is battery reading only (assuming it's fairly well charged).

[LanceM]

I'm with Arne, 12.5 isn't enough, I'd want at least 13 with the lights on otherwise the battery isn't being charged and you are running on an "even" type of voltage. If you start running the heater blower and the radio you might be on the - side of things. I'd pull it and have it checked, what the PO said and what the PO did may be two different things....

[texasz]

I would just take it to a shop (maybe even a parts store) to be tested...most will do it for free.

[boostedz]

Id do as Texas suggested, just take it to a parts store, its free bench testing and well, you will have your answer in about 2 minutes.