Charging battery drains over night must be a short somewhere

Tiny
TINGFISH
  • MEMBER
  • 1966 CHEVROLET IMPALA
  • 84,000 MILES
1966 Impala no AC- automatic-- When it rains, the generator light will come on. I know it is a short somewhere because it will drain the battery overnight if I do not disconnect the battery. I replaced the headlight wiring harness and the smaller firewall wiring harness- Someone advised me to replace the main wiring harness - and put a meter on the battery to see if it moves while I plug in items, one at a time--. I will try this and see what happens. I have added NEW grounding straps, and cleaned the metal where they touch.
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Wednesday, July 17th, 2013 AT 11:01 AM

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Tiny
CARADIODOC
  • EXPERT
Given the multiple symptoms I'd first suspect the voltage regulator. You might try unplugging it to see if that stops the battery drain.
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Wednesday, July 17th, 2013 AT 11:05 AM
Tiny
TINGFISH
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Well I replaced the (alternator), voltage regulator, horn relay, also-- Still does it-- I will replace the main wiring harness in a few days and I think that might be where it is at-- or another option is the high beam dimmer switch-- people have told me that if rust forms around the switch it can cause a short- because it is on the floorboard- I am hoping it it will go away after replacing the main wiring harness.
Thanks for the replay I will keep you posted

Tom
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Wednesday, July 17th, 2013 AT 3:27 PM
Tiny
CARADIODOC
  • EXPERT
Hold on. Throwing random parts at a problem is the most expensive and least effective way to diagnose a problem. There's absolutely no way the dimmer switch can cause a drain on the battery. If the head light switch is turned off, there's no current going to the dimmer switch. The switch could be shorted to ground, terminals shorted together, wires could be grounded, or anything like that and it wouldn't matter as long as the head light switch is off.

Same for the horn relay. That isn't doing anything, and if the horn works properly, it's unlikely there's anything wrong with the relay or circuitry.

Replacing an entire wiring harness is the same as tearing down your house and rebuilding it because one window is drafty. If a wire is broken or grounded or two wires are shorted together you will have other problems like a dead circuit, blowing fuses, or wrong things happening when you turn things on. It is extremely unlikely you will have a drain on the battery due to a wiring problem when there are no other symptoms.

Since your car is old enough to have no insane and unnecessary computers, tracking down a drain on the battery becomes real easy. The easiest way to start is by disconnecting the negative battery cable when you stop the engine, and reconnect it the next time you want to drive the car. If the battery is still dead, you have a bad battery and there's likely no need to look for any other cause. Also measure the battery voltage with the engine off, then again with it running. With it off, a fully charged battery will measure 12.6 volts. If you find around 12.2 volts it is okay but discharged. With the engine running the voltage must be between 13.75 and 14.75 volts. If it is low we will have to diagnose the charging system.

If the battery voltage is 12.6 when you stop the engine but much lower many hours later, disconnect the negative battery cable and connect a test light between the cable and battery post. You can use a digital amp meter too if you have one and know how to use it. If the test light glows, that proves there is current flowing and you do indeed have a drain. Start by looking for a glove box light or trunk light that isn't turning off, and an aftermarket radio that is wired improperly so it is not turning off. Also unplug the voltage regulator. Even though those parts are new, the regulator can be kept turned on when it should be off. That can result in up to a 3 amp draw which can easily kill a battery overnight.

If you haven't found the cause by this time and the test light is glowing, crawl inside the car and close the doors so the dome light goes off, then pull the fuses one at a time, and watch for which one makes the test light go off. That will be the circuit you need to follow.
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Wednesday, July 17th, 2013 AT 9:21 PM
Tiny
TINGFISH
  • MEMBER
WOW a lot of stuff was done-- I did most of what you asked. Yes, I disconnected the voltage regulator and it still drains. I did each item one by one- horn, horn relay, voltage regulator, alternator- I didn't mind replacing the complete wiring harness, as the wiring is old and brittle-- but you are correct-- it might be overkill for what I need to do--
I tested battery with the car running and it is around 14 v-- sitting it is 12+ volts- parked- I placed a meter at the positive side of the battery, and it reads voltage with everything off- I tested the glovebox and trunk light-- not there, they work properly- I disconnected the radio completely, just to make sure Nope wasn't that either-

-- I took out all the fuses-- and guess what? The meter still reads voltage with all the fuses out-- I don't know how that works unless there is a bent pin or something- at the ignition or a rusty floor high beam or something like that-
- I was wondering if a bad door pin to the dome lights could do this-- but no-- it would go out when the light to the fuse is off-
So I tried all of this, and still a drainage-- Haven't replaced the wiring harness yet-- so I hope that is it-- as everything else even removing all the fuses doesn't seem to work.
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Thursday, July 18th, 2013 AT 10:33 PM
Tiny
TINGFISH
  • MEMBER
More to the message

if it still reads with all the fuses out-- could it be a short AT the firewall plugs or panels-- the one with all the circuits-- there are two of these plugs-- one is a main plug/panel- and the other secondary-- I noted the secondary plug looked a s if it had a dent in it-- as if it were melted or hit? Not sure, the main wring harness I hope will replace the inner part of this--.
Anyway I'm still trying-- a s I want to keep this old bird-- Drives great, otherwise-- and that's what is more annoying.
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Thursday, July 18th, 2013 AT 10:56 PM
Tiny
CARADIODOC
  • EXPERT
It sounds like you're measuring voltage across the two battery terminals. You need to remove the negative battery cable, then insert an amp meter between the cable and battery post. If the drain is big enough you can use a test light too and just watch for the glow to go out.

One thing that is always still in the circuit after you pull all the fuses is the generator. It isn't real common to have excessive leakage in one, and even more uncommon for two to have a problem, but if you don't find anything else, remove the large output wire bolted to the back of it. Be careful to not let the wrench touch anything metal on the car while it's in contact with that terminal.
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Thursday, July 18th, 2013 AT 11:23 PM
Tiny
TINGFISH
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Yes I did that too and it still had a drain - so I believe it might be in the harness itself-- Will get a day off tomorrow or next day - and I will findout for sure--
What I plan to do is keep a meter on the negative side of battery terminal as you said--

Then I will hook up the main wiring harness-- with NOTHING connected to it-- on it and NO FUSES In The Fuse Box----If I still have a leak-- then I am pretty sure it is on the engine side of the firewall as you have suggested- a bad generator? Maybe--- I suspect that as soon as I hook up the wiring harness by itself-- the short will go away-- If it goes away- it would be on the passenger area of the car-- ()past the firewall)

This calls for another plan -- I will slowly add each plug and inspect the meter immediately after adding each plug. If the meter jumps immediately after adding a plug-- then I will know WHICH area of the car the short is located--
For example If I connect the plug (semi-circular) going to the steering column, and the short comes back (meter moves) then I I will suspect a short in the steering column-- this is my plan.
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Sunday, July 21st, 2013 AT 9:57 AM
Tiny
TINGFISH
  • MEMBER
Ok Hello Again I replaced the wiring harness and poof, the battery drain problem went away-- a new regulator (voltage) made the system charge-- I think the problem was at the fire wall- and is due to the fact that I went to an HEI ignition system, the original wiring system cannot handle the extra current draw needed to keep the HEI going.-

Runs smooth and strong now-- I have one more problem I disconnected the horn relay -- the battery wire is clearly marked for the horn relay- However, there are two more wires and I cannot guess which of the 3 plugs they go on to--- I looked up the wiring schematic in the service manual and I is hard to say which 2 remaining wires goes onto which one of the 3 plugs _ I guess I can tey a lot of combinations until the horn works-- eh?
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Tuesday, August 6th, 2013 AT 9:16 PM
Tiny
CARADIODOC
  • EXPERT
The HEI system won't overload the wiring. Breaker point systems draw a lot of current but only while the points are closed. I think you'll find the new distributor doesn't draw much current. The 12 volt feed wire in cars that came with them weren't any bigger than any other wires. A lot of people have upgraded to this system and using larger gauge wire has never come up in the discussion.

For your horn relay, every one I've ever looked at, at least on older cars, had three terminals. There's actually four wires but two are tied together because they both have constant 12 volts. Therefore, one relay terminal will have 12 volts all the time, one will read real low resistance to ground through the horns, and one will read 0 ohms to ground when you push the horn switch and open when you release the switch.
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Wednesday, August 7th, 2013 AT 11:57 AM

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