Won’t stay running if negative wire is pulled off

[turbopat]

Just wondering here... my car was acting funny yesterday like the voltage was low (no volt light). I turned it off at a safe place and it wouldn’t start again without a jump box. I got it running with a new alternator that I had and pulled the negative off... it immediately died... on previous cars this was the tell-tale sign that the alt was bad... I then bought a brand new one.... same thing? Is there something else that could cause it to immediately die?? Optima redtop battery


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[Chuck Leeper]

Optima redtop battery

Battery won't support the system, unless the alternator is working.
How old is the red top?
A bit of testing w/ a VOM will help.

 

[turbopat]

Optima redtop battery

Battery won't support the system, unless the alternator is working.
How old is the red top?
A bit of testing w/ a VOM will help.

Redtop is 2years old but just went through a test 2 weeks ago... I guess the battery could be bad now but... again, is it a good way to check an alternator in our car by just pulling the ground off the battery while running?


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[earlbrown]

I got it running with a new alternator that I had and pulled the negative off... it immediately died... on previous cars this was the tell-tale sign that the alt was bad... I then bought a brand new one.... same thing? Is there something else that could cause it to immediately die?? Optima redtop battery

Yeah, the voltage going nuts without a battery.

Unless you're running a carbed car with points, NEVER (EVER EVER EVER) remove the battery from the loop while the engine is running. And even then, don't do it.


With any luck you didn't damage your ECM or ignition module.

 

[turbopat]

So.. how do I test the alternator?


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[earlbrown]

With a voltmeter.

 

[turbopat]

With a voltmeter.

Gotcha lol. Do I check at the battery?


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[earlbrown]

Take a reading at the battery and the alternator (and the cigarette lighter).

Start the car and take a reading at the battery and the alternator (and the cigarette lighter).

While the engine is running, turn the lights on bright, the fan in high, the stereo up, open the doors.....

....then take a reading at the battery and the alternator (and the cigarette lighter).




Odds are you'll learn all kinds of stuff about the charging system and wiring that's 1/3 of a century old.

 

[turbopat]

I figured this out kind of.... I was able to jump a wire into the pink/black egr plug to the f terminal on the alternator... bam! Fixed! I think part of my problem is in the dash... I replaced the dash wiring... I believe I mislocated the ground for the cluster? My fuel gauge, dash lights, and turn signals don’t work...


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[MG8T7GN]

Isn't there something about if the volt light is not working, the generator won't charge? Caspers has a filed bypass harness to get it charging even if the bulb is out.

 

[earlbrown]

Yep. If you turn on the key and the volt light doesn't light up, it will cause a perfectly fine charging system to fail.


Worst design of a warning system EVER.

 

[Clark6]

1st I look at the date of the battery if its close to 5yrs,,,,,With Volt meter I pop the hood check the battery voltage by wedging the leads or gator clip better if can find a good connection, On the positive & negative posts. voltage should say 12.0-12-7 maybe..that range anyways...I leave the meter connected so I can read it, stick my arm in the car while reading meter, then crank... If it drops to like 8-10 volts on cranking I just get a new battery..... after cranking if not above 13.1-14.V I get a new alternator....worked for me in all my vehicles over the years others also. now if its a 2 or 3 yr old battery I look elsewhere for problem but so far haven't had to.

 

[Chuck Leeper]

voltage should say 12.0-12-7 maybe..that range anyways...I leave the meter connected so I can read it, stick my arm in the car while reading meter, then crank... If it drops to like 8-10 volts on cranking I just get a new battery.....

If the batt is less than 12.8, it's not fully charged.
If it is, and the volt drop is excessive, at startup, it could be other issues, such as volt drop across the starter sol, the batt cable connections, cable condition.
In the case of the Optima..Oh well.

 

[No disintegrations]

Yes 12.0 volts is discharged battery. Full would be 12.6 v with no load.
Over 13 v and you are charging but not much.

 

[No disintegrations]

Agree with chuck

 

[earlbrown]

In the case of the Optima..Oh well.

They are defiantly female.


I've learned that you can't just treat them like a normal battery, you have to tiptoe around them.



When this one finally dies, I won't be buying another.

 

[Clark6]

Yes I know the battery conditions vary mine was just baseline figures,,, good points Chuck on the drop across the other components...but so far haven't had those...( those aren't my only tests. I do it twice or the 1st time it won't crank & the age fits I get a new one. don't like being stranded lol. The longest battery I've ever owned was a Walmart Everstart,, lasted 8 yrs!! lol. 2012-2018. Just replaced it with a interstate megatron.