How to find a short and battery drain

[Larry B.]

Working on a '67. The battery was dead and replaced with a new one. After letting the battery sit overnight it was completely dead. I believe there may be a short in the electrical system. Car has all stock wiring that is in good condition.

What is the best way to find a short? Thanks

[Donald O.]

Re: How to find a short and battery drain

Larry,
You're going to need either a 12v test light or a good DVM.
Disconnect the neg battery cable at the bat and connect either the test light or DVM (set for amps) in series. and record the amps, a small spike is indicative of the OE clock winding itself. If you see the light illuminated constantly or an amp reading in excess of a few milliamps, you have a drain somewhere. But Where?
Begin by removing each fuse one at a time until either the amps drop or the light goes out. If this doesn't occur, begin disconnecting the alternator and the voltage reg.

My guess is the alternator has a bad diode.

DonO

[Larry B.]

Re: How to find a short and battery drain

Don, Once I disconnect the neg battery where exactly do I connect to test light? From the negative post to??

[Donald O.]

Re: How to find a short and battery drain

Don, Once I disconnect the neg battery where exactly do I connect to test light? From the negative post to??

If your test light has a clip, connect it to the neg cable and push the probe's spike into the battery post. You can secure it to the post with a small hose clamp.

DonO

[Domenic T.]

Re: How to find a short and battery drain

Donald is right on, and there is one that is not fused that can drain. The horn relay. Long time ago had a batt drain problem and did not hear the relay click when the key was turned on & off. The conacts were stuck together possibly fom a direct short.

DOM

[Edward J.]

Re: How to find a short and battery drain

Larry, once you have the test light hooked in parallel with battery, try un-hooking the voltage regulator, and the alternator after that. and make sure there is not a glove box light that is staying lite. These are a couple of common areas for battery drains.

[Larry B.]

Re: How to find a short and battery drain

When I hook up the negative cable, the voltage regulator makes a noise. Test light goes off when I disconnect the regulator with the test light in series. Replaced the regulator an it did not cure the problem. When I disconnect the alternator the test light goes off. Alternator??

[Floyd B.]

Re: How to find a short and battery drain

Another possible source of battery drain is a bad starter solenoid - on C-3's anyhow. The positive battery cable runs directly to the solenoid. I had this problem on our '73. Replaced the starter and the problem went away.

[Donald O.]

Re: How to find a short and battery drain

When I hook up the negative cable, the voltage regulator makes a noise. Test light goes off when I disconnect the regulator with the test light in series. Replaced the regulator an it did not cure the problem. When I disconnect the alternator the test light goes off. Alternator??

Yes. Alternator.

[Donald O.]

Re: How to find a short and battery drain

Larry, once you have the test light hooked in parallel with battery, try un-hooking the voltage regulator, and the alternator after that. and make sure there is not a glove box light that is staying lite. These are a couple of common areas for battery drains.

Edward,
the light must be in SERIES, not parallel. In a parallel connection the light would stay on, period. In series, you are trying to find where the short to ground is by removing the shorted item.

[Larry B.]

Re: How to find a short and battery drain

Larry,
You're going to need either a 12v test light or a good DVM.
Disconnect the neg battery cable at the bat and connect either the test light or DVM (set for amps) in series. and record the amps, a small spike is indicative of the OE clock winding itself. If you see the light illuminated constantly or an amp reading in excess of a few milliamps, you have a drain somewhere. But Where?
Begin by removing each fuse one at a time until either the amps drop or the light goes out. If this doesn't occur, begin disconnecting the alternator and the voltage reg.

My guess is the alternator has a bad diode.

DonO

Removed the plug from the voltage regulator and the test light went off. Replaced the regulator and no change. Removed the power red wire from the alternator and the light went off. Voltage reg makes a clicking sound every time I connect power to the alternator or plug unplug voltage reg. Should the light go off when I disconnect the alternator or regulator? And should the voltage reg make a clicking noise when power is applied?

Also may be unrelated or another problem. The power windows work with the key in the off position and removed.
What would cause this?

[Leif A.]

Re: How to find a short and battery drain

Removed the plug from the voltage regulator and the test light went off. Replaced the regulator and no change. Removed the power red wire from the alternator and the light went off. Voltage reg makes a clicking sound every time I connect power to the alternator or plug unplug voltage reg. Should the light go off when I disconnect the alternator or regulator? And should the voltage reg make a clicking noise when power is applied?

Also may be unrelated or another problem. The power windows work with the key in the off position and removed.
What would cause this?

Power windows are NOT supposed to work with the ignition switch in the "off" position. You may have found your power drain issue. When engaging the power window switch you are closing a circuit allowing current to flow. If the windows work with the ignition switch off and you're still getting power then you are completing a circuit that shouldn't be "hot".

[Dino L.]

Re: How to find a short and battery drain

This is how I find a current drain.....I take my Multi test meter, and select for DC amperage (amps), 10 Amp selection , I disconnect the ground cable from the battery, I connect the black lead to the battery post, and the red lead to the "removed " ground cable....this basically puts our ammeter in series.....you must be careful, do not start your car or use high current/amp devices like blower motor on etc.....turn everything off on your car.....the ammeter will show a draw....hopefully it will be in milliamps, (thousands of amps) if it reads amps you got a big problem, select the correct display scale to get it where you need it.....once you are connected and record the amp draw, go to the fuse block and pull one fuse at a time, and record what the mulimeter says, if no drop, then put fuse back and take the next one out....eventually you will find the circuit that is drawing excessive current and you will have to study the circuit diagram and check for frayed wires, poor connections and or failed devices on that circuit......last time I did it, the first fuse I pulled included the glove box door lamp......it was continuously on, 2 minute adjustment on two screws...fixed....Also, when I talk ammeter, I do NOT mean the dash mounted ammeter, I mean a hand held multimeter capable of reading amps. also note that the car pulls amps when the doors are open and interior lights are on, the clock is winding, god forbid you push the lighter in....don't do that while testing. You will find quickly......post a pic of your multimeter and I will comment on setting it correctly.

[Joe R.]

Re: How to find a short and battery drain

This is how I find a current drain.....I take my Multi test meter, and select for DC amperage (amps), 10 Amp selection , I disconnect the ground cable from the battery, I connect the black lead to the battery post, and the red lead to the "removed " ground cable....this basically puts our ammeter in series.....you must be careful, do not start your car or use high current/amp devices like blower motor on etc.....turn everything off on your car.....the ammeter will show a draw....hopefully it will be in milliamps, (thousands of amps) if it reads amps you got a big problem, select the correct display scale to get it where you need it.....once you are connected and record the amp draw, go to the fuse block and pull one fuse at a time, and record what the mulimeter says, if no drop, then put fuse back and take the next one out....eventually you will find the circuit that is drawing excessive current and you will have to study the circuit diagram and check for frayed wires, poor connections and or failed devices on that circuit......last time I did it, the first fuse I pulled included the glove box door lamp......it was continuously on, 2 minute adjustment on two screws...fixed....Also, when I talk ammeter, I do NOT mean the dash mounted ammeter, I mean a hand held multimeter capable of reading amps. also note that the car pulls amps when the doors are open and interior lights are on, the clock is winding, god forbid you push the lighter in....don't do that while testing. You will find quickly......post a pic of your multimeter and I will comment on setting it correctly.

Hi Dino,

That is a very nice description of how to troubleshoot this sort of problem!!! I would like to make one minor clarification to this statement:

"milliamps, (thousands of amps)"

I think you meant to say thousandths of Amps (1 Amp = 1,000 mA)

Joe

[Dino L.]

Re: How to find a short and battery drain

Thanks Joe.....yes, my typo, you are correct!!! Thousandths!