drain on battery

[timcrow00]

got a 70 c20 with a new battery that goes dead over night but last forever if you disconnect the cables. is there any common trouble spots that i should check first?

[norske]

Maybe the radio but don't know if it would be quite that quick. What I do is check the current draw on the batt and then pull fuses until the current drops. Then I know what circuit it's in.

[68gmsee]

Do a search on battery draining or something similar to get some more ideas, but I would start with checking the easy things first.

If you have a meter than checking the amps and removing fuses as norske mentioned is a good first start.

Things that you can disconnect for test purposes are any aftermarket components, like radio, cd player, amp, etc.

The alternator and/or voltage regulator can cause battery drain also. If you have the external regulator, disconnect it and the alternator. If it's the new style internally regulator, the diodes can cause voltage drain so disconnect it also.

Check for bad cables and connections.

[timcrow00]

tried pullin the fuses one by one and it never changed, but there is a defference of a tenth of a volt on my multimeter when i disconnect the battery cable. any other suggestions?

[Longhorn Man]

have you done any electrical work to it lately? Anything not working? It takes a good load tokill a fresh battery overnight.... a light would have caught your eys, horn working?

[timcrow00]

the alternator seems good had no change. not sure how to tell if its internal or externaly regulated. not aftermarket bs on the truck and i just bought it and tryin to work the bugs out of it. horn works but tail lights, radio, and heater fan doesnt work right now but shouldnt there of been a change when i took those fuses out if it was one of em?

[72BLUZ]

Originally Posted by norske

Maybe the radio but don't know if it would be quite that quick. What I do is check the current draw on the batt and then pull fuses until the current drops. Then I know what circuit it's in.

what he said

[mr48chev]

It sounds like it might be a bad diode in the alternator.
That would cause an unexplained drain like that.

Another thing that can cause a battery drain is a dirty top on the battery that allows current to flow across the top of the battery. Take your volt meter and hold one lead on the appropriate post of the battery and touch the other to various spots on the top of the battery. See if there is any reading. I have seen as much as eight volts flow across the top of a dirty battery. The cure is to clean it off.

The 70 will have an external regulator unless the alternator has been changed.

[Richard8971]

Mine had a similar problem. Found out my ignition cylinder was bad allowing me to take my key out at any time in any position. I was turning it all the way to the left to shut my truck off, leaving the accessories on all night, allowing the battery to drain. I never thought anything of it, just thought something else was the kulprit. The key should only come out when the truck is all the way off.

Got a new cylinder and problem went away!

Don

[68gmsee]

Originally Posted by timcrow00

... any other suggestions?

Originally Posted by 68gmsee

..... The alternator and/or voltage regulator can cause battery drain also. If you have the external regulator, disconnect it and the alternator. If it's the new style internally regulator, the diodes can cause voltage drain so disconnect it also.

Check for bad cables and connections.

-----------------------------------------------------
Try disconnecting cables mentioned. If you have time, disconnect all and reconnect one at a time until failure reoccurs. Then you know exactly what component failed.

Check on the radiator support drivers side and look for a small box with cables going to it. That's external regulator.

.

[Grapdawg]

I have the same problem. My ignition does exactly as descibed above. I can take the key out at any position. What part would I need to fix this. The ignition switch?

[68gmsee]

If you know the keylock number sometimes a new key will help, but more than likely it's just worn out tumblers.

Here's some good info from our resident lock doctor to help you out:

http://67-72chevytrucks.com/vboard/s...d.php?t=213860

[Grapdawg]

Good stuff! Thanks.

[Tynee]

The other thing that always gets mentioned when you start seeing electrical bugs, check your grounds. pull the screw out of each end of all the ground straps, clean both surfaces, and reconnect.

Also, I learned the hard way that a worn V-belt will turn the alternator, but will actually OVER charge the battery, I can't explain it, except to say that I wound up paying a mechanic $70 to diagnose and replace the belt. Check the edges of the belt closely.

Also, somebody mentioned the diodes of an internally regulated alternator earlier. Any of your local auto parts stores will bench test them, part of that test is checking the diode pattern.