Is it my battery, voltage regulator or ???

[hgs_notes]

Sunday I got my exhaust replaced, started the truck, took it for a drive, stopped at the gas station and it wouldn't restart. It just didn't seem to have the power to turn it over. The gas station is around the corner from my house so I bring over the burb and jump start it. I drive it home, shut it off, still no start. I let it cool down and put a charger on it, no start.

Now it sat a few days, no start after charger on the battery all day. Something really odd though is that when the charger is not on, the headlights won't come on. Turn on the charger, lights work. Did voltage check of battery and its low at about 12 volts. With charger its reading about 13.5 volts, which is about right to draw a charge. But no lights with 12 volts isn't right.

Could it be the solenoid on the starter, or the voltage regulator goofed up or just a weak battery? I haven't done anything but try the charger so far. It's just got me stumped.

HG

[69 Short Fleet]

With the battery DC voltage shd be right 12.6 DCV (this is important).
This is how fast in % your battery drops
12.6 = 100% Fully Charged
12.5 = 75% Charged
12.4 = 50% Charged
12.3 = 25% Charged
It drops that fast, if your battery is not up to spec (needs replaced) your altenator can not keep it charged as the voltage level on the battery is too low and your alt. can't make chicken salad out of chicken poop (so to speak). I'd clean all your baterry cable contacts with a wire brush until their shiney and insure they are tight. After boosting your truck and disconnecting the cables through a DMM (digital multi-meter) and measure the terminals on your altenator and then on your battery (the 2 main studs pos. & neg.) and check your voltage you shd. be getting around 14 to 14.5 DCV at the terminals. These are the first things I'd check however it could be other issues causing your problem. Hope this helps. Doug

[blaserman]

Then there is the old way. Get the truck running and remove a battery term. If it stops it is the alt, if not battery

[Lemield]

Originally Posted by blaserman

Then there is the old way. Get the truck running and remove a battery term. If it stops it is the alt, if not battery

My 2 cents worth....That's about what its worth too!

Years ago I worked in at an auto parts place and we would do the same thing. If you disconnect the positive cable and the truck dies, then the alternator is bad. If it keeps running, then turn on lights. If it dies then, the regulator is bad. This has always worked for me on old vehicles.

Apparently, it's not a good test on a computerized vehicle...at least thats what I've been told.

Oh...also, DON'T hook the cable back up while it's running. Could damage alternator.

Good luck.

[VetteVet]

Originally Posted by Lemield

My 2 cents worth....That's about what its worth too!

Years ago I worked in at an auto parts place and we would do the same thing. If you disconnect the positive cable and the truck dies, then the alternator is bad. If it keeps running, then turn on lights. If it dies then, the regulator is bad. This has always worked for me on old vehicles.

Apparently, it's not a good test on a computerized vehicle...at least thats what I've been told.

Oh...also, DON'T hook the cable back up while it's running. Could damage alternator.

Good luck.

Yeah and don't rev the engine with the battery disconnected and the lights on as the alternater may go to full output and blow both the headlights. Ask me how I know.

[flip66]

Some batteries will show a charge and as soon as put a load on them they will lose all voltage as soon as the load is removed it will show charged.

[RainFade]

Get a digital multimeter.
Put it on the battery with the truck not running, make note of the voltage.
Start truck, retest with running voltage should now be 13 volts or so if so alt is charging. If little to no change or even slightly less voltage then you are not charging.

[fastwillie 696969]

old school check for altetnator is to take a magnet and see if it sticks on the back of the alternator bearing cap on the back once you start the engine

[modifiedGMC]

Originally Posted by 70blowngmc

old school check for altetnator is to take a magnet and see if it sticks on the back of the alternator bearing cap on the back once you start the engine

I think that should be, stick something metal like knife blade or screw driver to the back of alternator and IF it magnetizes it , it's charging. If you just stick a magnet to the back of the alternator it will stick even if the alternator is on the ground because the bearing is steel.

[hgs_notes]

Thanks for all the tips guys. I had to jump start it today for it to do anything, acted like there was no battery. Got it running, removed battery cable, it hesitated, but ran. Checked the voltage of diconnected battery and its about 12.5 volts, checked voltage on alternator and its about 13.2v. Turned on the headlights and it almost died, then kept running. I cycled the headlights again a few times and it ran fine, no hesitation. Put the battery cable back on and parked it. Shut it off and now it restarts fine.

Is it possible the voltage regulator was stuck some how, and drawing a full load without the battery jolted it awake?

I'm getting the whole system checked tomorrow.

HG

[VetteVet]

My guess is you had a poor connection at the battery cable so it would work until the lights were turned on and then not work and the charger would push enough amps through to light the headlights. When you removed the cable to check the alternator then put it back on the connection was good enough to work as it should.

[SweetandLong68]

Originally Posted by RainFade

Get a digital multimeter.
Put it on the battery with the truck not running, make note of the voltage.
Start truck, retest with running voltage should now be 13 volts or so if so alt is charging. If little to no change or even slightly less voltage then you are not charging.

When it is running shouldn't it be a bit higher than 13? More like 14-15 volts? Just wondering.

lata
CHRIS