A couple days ago I noticed my alt was not charging at one click above 13 on the dash voltmeter, as usual, but more like 12volts. Today it was down to about 10 volts as I drove off to work. Almost turned around to get the daily driver, but didn't want to be late. After work, stopped at National Auto, had the battery tested, it was at 12 volts. Drove home, 15 more miles, and tested battery, now at 11 volts.

Even thouigh the battery tests at 12 volts with my analog tester, the voltmeter in the dash now says 9 volts (just on the edge of the yellow warning area, whatever that voltage is), both with the engine, running, and also when the engine is off with the key "on". Why is the dash voltmeter different from the actual battery voltage ?

At first I thought my alt must be not charging at all, and that the 11, then 10, then 9 from the dash vmeter was the battery voltage slowly dropping as I sucked up battery by driving. But apparently not.

My guess is that I need a new alt, but I don't understand the dash voltmeter readings.

 

the alternator itself generates a power current. The battery (in a generic way of stating it) is just to power the starter to fire the engine, once the engine is pumping fuel and firing turning the pullies, the alternator belt is turning the alternator and then basically the car runs off the alternator as the alt... also charges the battery again and makes its own power, your volt meter is not testing the voltage from the battery but from the alternator..

Battery should be around 12 volts (your reading) but the alternator is only pumping out 8 volts, which it should be around 13 volts.

They are two seperate things that power different current of voltages. face it, if something else didn't control the re-charging of the battery, how fast do you think the battery will last when your headlights are on? There must be something else to power all your features/lights/etc etc while letting your battery take a break n charge...

get what i'm saying?

 

Hydric,

Yes, I understand what the alternator is for. What I don't understand is why the alternator reading is going down so gradually.

Also, why is the dash voltage reading the same when the engine is not running ? The alt isn't putting out ANY current with the engine off, so why would the reading still be exactly the same as with the engine running?

Example : I get in car, turn on key, not starting car yet, see dash volmeter reading 3 tick marks below 13. I then start car, and dash voltmeter STILL is exactly 3 tick marks below 13.


Seems to me the dash voltmeter is getting nothing from the alt, since running the alt has no effect on it.

 

Heh, try thumping the dash face plate with your fist right over or next to the volt guage, it may just be a flakey connection with the guage.

With the car running hook your meter to the alt and see what it is putting out, if it is less than 12 volts it may be on its way out (could just be the regulator too), if it reads 9 volts or lower it is definately dieing.

 

oh i understand your question... sorry about that useless newbie info u already knew.

My volt meter is off, and as morley said i tap the gage and it shoots up, sometimes if u gently push above it too it goes up...

again, sorry for the misleading crap...

 

Well, I also have the real slow wiper blades and the real slow turn signals so I don't think it's just a guage not reading right.

Where would I hook up the pos and neg of my voltmeter to the alt ?

 

Positive goes to the red lead on the alt and neg goes to ground.

 

if you've always had slow wipers I would check the fuse, i think it requires a 20 amp but in mine i had a 15 and it was slow, put a new fuse in and she works... i don't have the delay but oh well, no miss there..

 

No, the wipers are slow now that my dash voltage is reading low, which makes me think that the dash voltmeter is right, the voltage IS low, and that's why the wipers are slow and why the turn signals are slow.

I'm going to check the wiring from the starter today, since I had some rewiring done there a few weeks ago, and I think one of those wires is related to the alt. If I don't actually find a wire hanging loose, I'll hope those wires are OK, then I'll check the alt with my voltmeter.

I just need to know where to hook up the leads to the alt.

Maybe I can just test the volts on the battery with the engine running ? But that would just test the battery voltage, probably.

 

connect the + lead of your meter to the red wire that has a 10mm nut holding it on... the wire is all by itself... Now connect your black lead to a ground... if your alt. is putting out less than 14. volts you have a problem.... check your fan fuse before going to get a new alternator, because the charging system on some (maybe all? ) of our cars went through the fan fuse... I wasted 3 hours testing because that fuse was bad one time haha.

 

Quick_Trans_Am,

Thanks for the how-to about testing the volts.

The fan still comes on when the temp is 220 F, so the fan fuse seems to be OK.

I called the mechanic who did the soldering on some wires under the dash a few weeks ago, and he says he doesn't think they are realted to the alternator problem. Yeah, I hope it's just the alt, and not some other electrical problem !

Thanks,

GTA88

 

I just jacked up the car and checked the wires at the starter. Look normal, nice and tight. Tested the alt as you said, with the car running, and got exactly the same reading as I got at the battery with the car off (11 volts), so I'm taking the alt out to have it tested at Autozone, just to verify it's bad, then I guess I'll end up getting a new alt somewhere.

Thanks to everyone for the help.

 

DId you grab the starter wire n stuf and see if you can wiggle them???

I found outthe last time I got a starter, they did not tap the hole that hoel it together deep enough, so the whole end cap where the wires were would wiggle. It did that heat soaked thing on me but one wiggle figured it out. I tried to tighten the bolts but they did not tap them deep enough. I replaced it with one that was all nice and tight and no problems.


It could be the same kiind of thing but the thread were tap a little more but still not enough.

Matt

 

Yep, everything's tight down there at the starter.

My old alt tested out at 1.9 volts, pretty low, so I bought a new alt to install.

But when I was tightening down one of the bolts in the back of the new alt, that holds the battery wire, the bolt head snapped off! and the threaded shaft is stuck in the hole. This will be fun to fix. So close yet so far.....