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Dumb question about finding a short
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DRR Sportsman
posted
I have a 1960 Chevrolet pickup and I’m having an issue with something draining the battery.
As long as I start it every day or two and drive it a little I don’t have any trouble, but if it sits more than a few days the battery will be dead when I go to start it and I have to boost it off.

I’ve check the battery and it’s good. The alternator is new and I have checked it and it is charging good. It has to be that there is a short draining the battery.

Could anyone give me an idea on how and to find the short. There are several good mechanics in our small town I could take it to, but I like the feeling of fixing something myself.
I appreciate any and all help.
 
Posts: 398 | Location: a race track near you | Registered: February 12, 2007Reply With QuoteReport This Post
DRR Sportsman
Picture of 369dragster
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You will need an amp meter or a test light. Pull one of the battery cables off and put the meter between the cable and the battery(one lead on the cable and the other on the battery). If it has a draw the light will light up or the meter will read the draw. Start pulling fuses or unhooking accessories till the light goes off or the meter goes close to zero. That will tell you where to look, then wiring diagrams come in handy to chase wires.


Ken
 
Posts: 319 | Location: Massachusetts | Registered: March 15, 2007Reply With QuoteReport This Post
DRR Sportsman
Picture of FootbrakeJim
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First thing, even with a newer Alternator, they can leak current through a defective diode. Disconnect the heavier "charge" wire from the alt and see if that stops the drain. (Cover the wire end with electrical tape to keep it from contacting ground).

Have you tried the old method of pulling fuses? pull the negative cable off the battery, connect an Ammeter, (or multimeter in Amp / Current range), inline between neg terminal and cable, and measure current drain. Then either pull fuses 1 at a time, and recheck current flow after each fuse is pulled, when you pull one and current drops to zero (or near it), you have isolated the likely circuit that has a short in it. Or, pull all the fuses out, check current flow, (hopefully zero amps), then begin to reinstall them 1 at a time, until you see the current increase. Check that circuit of the fuse that causes the current flow to increase.

Couple of notes:
1. Save some time by writing down the fuse rating for each circuit as you pull them, so you put them back in the correct spot.
2. Old vehicles like that shouldn't have items that cause a constant drain, other than the clock, and maybe an aftermarket radio. My son has an added stereo amplifier in his truck under the back seat, and it drains his battery if it sits for a few days or so.
3. If you pull all the fuses out and still see current flowing on your meter, there is possibly a short elsewhere in the wiring. Try disconnecting the Alt charge wire again, see if that stops current flow. If not, begin tracing the starter wiring, and the headlight wiring, (neither of those circuits run through the fuse box). Lastly, look at the supply wiring that carries battery power to the dash, horn relay, voltage regulator circuits.

This method has worked for me over the years, on older vehicles. It begins with the most likely circuits, ending with the less common problem areas.
Until you identify the cause, best disconnect the ground cable so that a possible short doesn't burn up your truck.


Dan "Jim" Moore
Much too young to feel this damn old!!
 
Posts: 1029 | Location: Farmersville, TX  | Registered: December 05, 2002Reply With QuoteReport This Post
DRR Sportsman
Picture of FootbrakeJim
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Ken tree'd me. Big Grin

One other note: If your truck is a '60, I believe it could have originally had a generator, rather than an alternator? If there have been ANY modifications or repairs to the original wiring, that is a good place to begin looking for issues.
Not too many 60+ year old vehicles with 100% virgin wiring in them. I have seen well-taped splices and beautiful heat-shrink tubing covering wire connections that were twisted together, with a stray strand sticking out that would intermittently touch a metal surface and short out.
The old mechanical voltage regulators also would occasionally short out internally. If yours has one, try unplugging the connector and check your current flow.


Dan "Jim" Moore
Much too young to feel this damn old!!
 
Posts: 1029 | Location: Farmersville, TX  | Registered: December 05, 2002Reply With QuoteReport This Post
DRR Sportsman
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One thing I ran into with my golf cart and a new radio where it was draining the battery after a week. I ran 12 volts direct to the radio power line and the yellow wire for the clock. Turns out even with the radio off, it still used power. Added a switch to the 12 volt supply and problem was solved. Clock was left wired direct.

This message has been edited. Last edited by: J Olejniczak,
 
Posts: 293 | Location: New Milford, CT USA | Registered: December 14, 2003Reply With QuoteReport This Post
DRR Sportsman
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As mentioned above I have found some aftermarket radios do have a steady draw even when off. Its not a lot but it can drain the battery over a few days of sitting. If this has one I agree with starting there. Unfortunately its hard to work around it if you want to maintain your presets and clock on the radio. About the only solution of I have come up with is a battery tender but thats not always convenient.


B.J. Masiello
 
Posts: 250 | Location: Connecticut | Registered: November 27, 2007Reply With QuoteReport This Post
DRR Trophy
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Ditto on the alternator diode trio, especially the 10 and 20 SI models. Have changed a mess of them in the day.
 
Posts: 290 | Location: Nevada | Registered: February 01, 2009Reply With QuoteReport This Post



DRR Sportsman
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My radio presets stay with the yellow wire for the clock still wired all the time. Battery now has lasted for weeks this way.
 
Posts: 293 | Location: New Milford, CT USA | Registered: December 14, 2003Reply With QuoteReport This Post
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