What is the most common cause for the interior voltage gauge to run 8V-12V depending on electrical load while during the same loads, the voltage at the batter is a full 14V? I had suspected the alternator, but if the battery sees 14V, I imagine it's charging okay.

Sometimes (very rare these days), the volt gauge in the dash will read 13-14 or so, but all it takes it a tap of the brake pedal, and it goes down. If the turn signal and headlights are on, the brakelights will put the needle on the edge of the red zone (8V?). But even then, the battery itself is showing 14V.

Thanks.

 

It's either a bad battery not holding a charge or the alternator not putting out enough current. You need a load test on the battery to properly test it - most chain auto parts stores will do this for free. I'd get both tested.

 

If I tell you I have to boost it off if it sits for more than two weeks, I bet you'll suspect the battery even more. The last two times I boosted it off, I had to let the boosting car run for several minutes before the GTA would do more than just click. The car sits a lot, and I know that's not good on the battery.

Do the Optima batteries resist failing from age +long spells of sitting up better than regular batteries?

 

large voltage drops are the result of high resistance in connections or wires.


Even so, a bad battery can still show 14 volts unloaded and be bad. Put a load tester on it, pull some current, and see if the battery can keep up.

 

It drops to about 12.5V when the headlights, brakelights, turn signals, and heater on. I will get it load tested at a store this weekend.

Thanks for the help.

 

Car off
Measure voltage at battery terminals (12-13v)
Turn on headlights (measure voltage, ideal would be less than .2 volt drop)
Turn on radio accessories (same as above)
Electric fans (now here is a lot of drain)

Monitor the voltage for about 5-10 minutes. It should not drop more than 1volt total (less than 12v). If it fails that, battery is most likely going out, or your alt isnt doing its job. But you mentioned that it only happens if it sits. The alt is probably working fine.

Good luck

 

Autozone tested the battery and alternator, and said both were fine. The device was handheld, and not on the roll-around cart. I'd never seen that small device before. For now I'll trust their readings.

Time to hunt down all the grounds I guess.

 

I work at an Autozone, and I've never seen a handheld device capable of load testing a battery and charging system. It may have been a voltage gauge or something of that sort. When we load test a battery we put a 500-550 amp load on it which creates alot of heat, so I doubt they tested everything with the proper tool. I would go to another parts store and have them test it. my $0.02

 

Yeah, the thing was the size of a scan tool, and the leads were over 5' long. What kind of load can THAT put on a battery?? I saw the roll-around device in the store. Apparently this dork doesn't know what he's doing. For the alternator test, I was told to hold it at 1,500 rpm. I'll go to another store as you suggest. There's an AZ in every direction. Hehe.

 

The voltages you mentioned indicates the engine was running and still you got only 8 to 12 V at the guage. This isn't a problem with the battery or the generator. Both would have to be bad in order for this to happen, and then of course you wouldn't be able to start the car... It is like Toehead says; there's a bad connection somewhere. Do you notice if any lights or accessories vary in strength together with the guage? If not then it could be just the guage itself that's on the fritz..
Btw.; modern electronics are fully capable of measuring the inner resistance of batteries without having to resort to huge load resistors, only it wouldn't say very much about the capacity though..

 

You might want to check the actual gauge itself.My 88 Camaros voltage gauge was reading low and I was ready to replace the alt but after testing it was working fine.My mechanic suggested I replace the gauge and upon doing so it now will read 13 + volts

 

Things do dim or slow with the gauge. When it is dragging down near 8V, the turn signal flashes very slowly. I think a connection somewhere is to blame. That will be my next chore. Is there any place/area best to start looking first?

 

Well, it's me again. Since this old thread was started, I think the battery has been replaced, but as most suspected, it was not the issue. I have added "The Big Three" ground cables, too. None of that worked. I still saw the same symptoms.

Yesterday I drove the GTA on my club's poker run. On my way home, I suddenly realized the voltmeter was a tick over 13V. After I got closer to home, I turned on the lights/foglights, ran blower on high, had radio on. It was warm enough the fan was coming on at stoplights, too. The voltmeter settled down a tick to 13V even while driving. Only idling would make it drop ONE tick below 13V. For the last few years, that same load and idling would have it down to an indicated 8-9V. I also noticed the turn signals were flashing faster.

I know as soon as it became "right" again, it can go back to the way it was.

I am wondering if there's anyone here that since this thread was started has dealt with anything similar and figured out a solution.

Thanks.

 

I am having the exact same problem with my 88 5.7L Iroc. I have replaced the battery and had the alternator checked and all is fine with them. When i bought the car it had an accel coil and with that installed it would actually go so low the car would stall and die. I replaced it with the stock coil and i stays running but i have the same symptoms as you , very low voltage. I can see the lights dim and get brighter when i give it gas. If i let it idle for 10-15 min it gets so low it sounds like its about to die. Any help would be great thanks!!

 

I had a similar issue. Follow the wiring in the starting circuit. Make sure the connections are clean. It could be as simple as the feed into the alternator being dirty and not allowing enough of a current. You can check with a multimeter to see if there is power going from the alternator when it's running wit one line on the alternator out bolt and another like on the intake or something. just as long as it can acomplete a circuit. if you see less than like 13 your alternator isn't getting power, assuming that it's been replaced/tested /etc etc. I know that I had an issue like that when my wiring wasn't making a good connection and was running solely on battery juice. Once I traced down the problem, the alternator was pumping 14.4 and I haven't had a problem since. I do have a hot start problem now that needs attending (damn headers!)

 

Would it help to say that when i give it gas the gauge moves back to 13 and lights get bright

 

That would imply that the alternator is doing its job. What exactly have you tested/ruled out?

 

I removed the accell coil and replaced it with the stock one. That helped it from dying while idling. It now just idles down near 9 and with headlights on it goes into the red. Until like i said when i rev it. I have also unplugged one fan to help with the load. I had the alternator tested and got a new battery. Im not very comfortable with electronics thats as far as i have gone.

 

I've got a similar issue with my '87. I'm leaning towards an intermittent short in the wiring somewhere which will be a real b*tch to track down. My wiring was butchered when a PO installed an alarm system. Trying to undo that without totally disabling the car's electrical system is going to be tricky.

Anyhow, I've spent the last 4 years totally rewiring & debugging the electrical system on my boat. I had almost the exact same problem, 6V at the dash gauge. I eventually figured out the boat had a wiring harness for twin engines but mine only had one. Someone who worked on the boat before I got it wired everything to everything which caused a dead short at the coil. The result was a fried coil & electronic ign module ($700 cause it's a Volvo Penta). I traced every wire and every connection and those I couldn't find a use for I clipped out. No more problems on the boat.

Looks like I'll be tracing & splicing to fix it.

 

You check your grounds? make sure they're clean and the battery cables are in good condition?

 

The ignition switch can be the culprit too. My old '66 GMC pickup ignition switch had enough resistance to stop the starter solenoid from working. It also caused the same symptoms being mentioned. Some PO wired a pushbutton fed straight from the battery and tied into the starter solenoid wire.

 

Ive seen alot of replies mentioning the grounds. Battery ground is nice and tight and the mesh ground going from the block to the fire wall is in good condition. What other grounds should i be looking for?

 

Anyone figured this one out yet? My 87 IROC has the same issue. New starter/alternator/battery/cables/grounds. All volts under the hood checked and verified to be 13.7v+ at all times no matter what accessories are running. Volt gauge will show 11-12 volts with lights on idling at around 650rpm and stepping on the brake pedal drops it to 9v. Tried everything suggested in the thread (besides rewiring the whole dash). Anyone have any additional ideas???

 

Given afremont's post, did you do any testing on the ignition switch? Any idea how to test it?

I don't know if it's my imagination or not, but it seems the last two times I drove my GTA, the voltmeter reading was somewhere in between the bad/extreme readings I've become used to and the normal reading I had for one short drive a month ago...

 

Not sure on proper testing procedure for ignition switch. All I did for that was make sure of continuity and check the resistance between power and switched 12V...nothing showed on my meter for resistance between the two wires...

 

What were your points to measure? Electrical stuff intimidates the crap out of me. I am clueless with this stuff. I rather be turning a wrench than poking a multimeter around.

 

You really need to measure for voltage "across" the switch with the key on. Since there is so much stuff running from the switched power, it would only take a tiny amount of resistance (only a fraction of 1 ohm)to cause a voltage drop of a couple of volts. Ideally, the key switch should be of zero resistance and not drop any voltage. You put the meter in voltage measuring mode and put the red lead to the wire (red?) feeding the key switch, you put the black lead on the output side of the key switch (pink wire?). If you can measure the "missing" voltage (1-3V) this way then the ignition switch is bad. If not, then the switch is good and you have a bad body ground.

 

I guess we do that by finding those wires coming back out the base of the steering column with the kick panel removed? Is the proper thing to do is poke through the wires' insulation with the MM leads? Or try to follow the two wires to some connector and stick the leads there?

Thank you for the explanation above!

 

This problem is likely due to a poor main electrical connection. This includes main positive wires, main negative wires (ground), and the main negative wire to the engine block.

Check for clean tight connections on all main wires.

Do a voltage drop test...
http://www.engine-light-help.com/voltage-drop.html

 

I had a low volt reading on my gauge and it was a bad connection on the back of the gauge cluster so check all the connections on the gauge cluster also .