Reproduction Parts for 1916-1964 Chevrolet Passenger Cars & 1918-1987 Chevrolet & GMC Trucks


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ABowlin Offline OP
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I’m no electrician, so looking for aid on how to find what is draining the battery. Is there a best method to track a short? Would love to leave it connected instead of hooking it up / unhooking it every time I want to drive.

Thanks.

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You can disconnect each elerical item one at a time some as simple as removing the fuse.
This includes disconnecting the generator.


Gene Schneider
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Does your ammeter indicate a discharge when everything is supposed to be off? That should be a great indicator.

What car is having this problem?


Rusty

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ABowlin Offline OP
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Hey Rusty, this is for my 33 1.5 truck. It’s always had a short since my Dad restored it 25+ years ago. Only the temp gauge works, so going to start with the gauge wiring first.

Are you thinking I should turn it off and start seeing what is still giving off power with my ammeter?

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Remember that on these old Chevy’s the temperature gauge and oil pressure are mechanical gauges. There are no electrical connections needed to make them work. Think of this. The temperature gauge still registers engine heat when the engine is not running.

I am suggesting that the ammeter in the instrument panel should show “neutral” (no charge or discharge) when the ignition is turned off and none of the lights are turned on.

One big assumption I am making is that the vehicle is wired correctly. This means that all of circuits are connected like they were when it left the factory. Perhaps a good staring point is to simply start tracing wires and connections. Compare them to the wiring diagram in the shop manual.

I am not an expert on the ‘31 wiring so hopefully one will jump in if I am not correct. Based on what I see in the wiring diagram, everything that requires electrical power except the starting motor should be wired through the ammeter. The generator should also be wired through the ammeter.

So if the ammeter shows neutral and the battery still runs down, the short or connection to ground is between the battery and the battery side of the ammeter.

Another way to start troubleshooting is to disconnect the ground wire on the battery and connect a volt meter between the battery post and that cable. There should not be any voltage. You can also connect an test ammeter between the positive battery post and the cable to the starter. There should not be any current going through the meter until you turn on the lights or ignition.

BE CAREFUL when you connect your test ammeter this way. You can easily overload the ammeter in your volt-ohm meter.


Rusty

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Sticking points in your cutout can cause this also.


J Franklin
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If the points in the cutout stick that will show as full scale discharge on the ammeter…with a lot of smoke!

Experience can be a painful teacher!


Rusty

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Originally Posted by Rusty 37 Master
If the points in the cutout stick that will show as full scale discharge on the ammeter…with a lot of smoke!

Experience can be a painful teacher!

That didn't happen on my car, just a dead battery the next day. I did see discharge on the ammeter after I figured it out. A diode can be installed in the cutout case instead of points.


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You need to start disconnecting various circuits while watching the ammeter. When the ammeter goes to neutral you know which circuit to investigate more.

You only have 3 circuits that use electricity: lights, ignition, and horn. Have you looked to make sure that the brake light does not stay on? Those switches will fail in the closed position. I am sure that you had turned the ignition switch off. That mistake never happens.

I really do not expect the cutout is the problem. If those points do not open the full power of the battery is immediately sent to the field coil in the generator.


Rusty

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ABowlin Offline OP
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Rusty,

Haven’t had a chance to check yet. But I know the lights don’t stay on. The horn hasn’t ever worked, so wondering if that’s the culprit from 25 years back. My dad installed a push button on the dash for the current horn, as he couldn’t ever get the main horn to work. Ill double check the ignition with the ammeter as well.

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That is an easy check - just remove the hot wire from the horn and check the next day,


Gene Schneider

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