voltage drop when keyswitch on

[rsefczek]

a very frustrating development. i have replaced a faulty voltage regulator recently. today when i turned the keyswitch i got nothing, no click, no starter, no noise, no ammeter light (but faint oil light). when i check the battery it reads 12.8 V., at the stud on the solenoid it reads 12.8V, on the alternator it reads 12.8V. but when i put the keyswitch to the on position they ALL drop to 4V. what would cause this voltage drop (including the reading at the battery terminal???). help!

bob

[baz]

flat or dead battery its got volts but no amps have it tested

[rsefczek]

i'll pull the battery and have it tested, baz. but i'm curious to understand why the voltage drops with the key on?

[rsefczek]

btw, i saw the highlights of the fulham sunderland game on tv. just a bit of snow there, eh?

[baz]

snow the last 2 days yesterday i was fishing for trout in the snow ,not one of my better ideas , but we can get snow here in june


the voltage drop to me would say that the battery just wont hold any amps so when you put the load on to it from the coil (the main draw of power till the starter spins with every thing turned off) it just kills the battery dead
the other pull on the power is the alternator but even a dead short inside that would be obvious (smoking wires and smell of burning) so i think its just the battery

[jeff denton]

You need to load test the battery. This is always step one. If it passes a load test, start looking at connections, from the battery back. All grounds are part of the circuit, too, remember to look at all of them.
If something was drawing a good battery down that much by turning on the ignition you would have something getting very hot, quickly. Even cranking the engine shouldn't pull it down that low! If, that is, all the connections are OK.
Quite often the culprit will be right at the battery terminals. Clamping your voltmeter to the battery cables will not catch actual readings in this case, you are not really monitoring the battery itself, see that? So do clean these up first, eliminate that possibility right there.
If these steps don't help, let us know, we'll scratch our heads a little harder.

[rsefczek]

thanks jeff. before i posted i went through as many of the old posts as possible. after reading them, i checked/cleaned all the grounds, pulled the battery cable and cleaned the terminals (as well as the cable connects). still had the voltage drop and no click or starter when turning the keyswitch to start. at first i was worried my switch had gone. to be honest, i hope baz is right and it's the battery (although i do have headlights, parking lights, etc. which makes me worried that it's not the battery....) things that make you go hmmm.

bob

[asdasc]

I would unplug the new voltage regulator and try the ignition switch. If you got that wired wrong, it could be shorted inside. Of course, with a good battery I wouldn't expect it to stay shorted for long. Most of the stuff inside a voltage regulator would pop open like a fuse with a direct short on a full battery. You get lots of current that way. The other thing to do is to put the car in gear and push it an inch or two (or just turn it with a wrench on the end of the crank). Sometimes if you have a worn spot on the flywheel the solonoid can get jammed in there and not work. Feel the starter, both the big part and the solnoid, does it get warm when you do this?

Like Jeff said, if we haven't found it yet, let us know and we will come up with more work for you!

I agree with Baz, though, my first test would be a load test on the battery. Any autoparts place will run it for free, just carry the battery in. I know Autozone near me does it.

[jeff denton]

Oh, the headlights do come on? That changes things. What does a headlight load do to battery voltage? It should draw more than the ignition.
Need to know what battery voltage is with headlights on.

[rsefczek]

went back out and reconnected the battery (getting ready for a run to autozone for testing tomorrow). with the lights the voltage at the +terminal drops to less than 1 V. i'm so confused....

bob

[jeff denton]

I say it's the battery that's causing you the grief.

[maglinjosvinn]

think about this:

try your local auto parts stores. most do free testing on batteries and whatnot for you, and they're ... 90% right each time. lol. *has had a couple screwups* but enough to go on usually.

u hshould be able to just take the battery in and have it tested no problemo.