Battery drain?

Still have the drain but I don't think it's under the hood. 2wires come from a single pole off the back of the alt. 1 goes to pos battery and the other goes to the light switch, which is connected to the ignition. Thanks

 

Why does it go to the light switch? The light switch is always hot is it not? Shouldn't it go to the "on" position of the ignition switch?

 

Remove the one going to the light switch. You only need the one source from the battery.

 

I got the new alt checked and seems to be running perfectly. The drain is very small ( barely lighting the tester) and is almost something I can live with. For a short time there was no drain after I took apart my light switch and ignition and put it all back together. I'm convinced the problem is in the dash now and will continue to investigate. I'm thinking if a diode in the right place may help. I appreciate everyone's help. I'm learning a lot!

 

Do you by any chance have a clock or a radio that has a clock in it? Any add on stuff we don't know about?

 

Remove the one going to the light switch and ignition switch and re-check. If the light still lights denoting a draw then there is an issue with the alternator from what you describe. An alternator can test fine but still be "leaking" current causing a draw on the system. I've run into this many times with 10si alternators. The internal diodes get weak allowing enough of a draw to run the battery dead but can test fine on a machine the local flaps use. Many of their testers check for output, but not total output, condition of the diode trio, or the regulator.


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"I'm thinking if a diode in the right place may help"

Except most typical diodes cause a forward voltage drop (about a one to one-and-a-half volt loss).

 

And remember. Just because the part is new, doesn't mean it is any good.

 

A silicon diode (what the common diodes are) ideally has a 0.6V barrier potential.* If the voltage drop is not 0.5 to 0.7 V, there is something wrong with the diode. And it is not a resistance - it's a constant drop regardless of current.

Anyway, the drop won't matter because, on a unitized Delco, the diode goes in the wire that energizes the field to start the alternator charging. The voltage on that wire just has to be enough so that the alternator can make its own voltage. Indeed, that's why a diode (or a resistance) is needed there - because once the alternator starts working, it makes its own field voltage and that's what back-feeds into the ignition through the switch connection.

And if you have to put the diode somewhere else to block back-feeding (not sure where that would be...) the drop is not significant compared to the range of voltages that your electrical system sees. Running on battery power, you are ideally at 12.6V, but the level of charge on the battery causes that to vary some. And when running, you will typically see between 13 and 14V. So the normal range is a few times the drop you'd see from a diode.

I would not hesitate to use a diode, if I had a good reason to add one. But there's no place for one with a one-wire connection, which the OP says he has now.

*Germanium diodes have a smaller 0.3V drop. Germanium diodes were developed before silicon diodes, and would be in wider use if they were as cheap or as robust as the silicon parts. You sometimes find germanium diodes in old radios and TV sets. You can build a "crystal" radio with a germanium diode pretty easily - look on the net for instructions.

 

"Except most typical diodes cause a forward voltage drop (about a one to one-and-a-half volt loss)."

"silicon diode (what the common diodes are) ideally has a 0.6V barrier potential."


I guess I was thinking of diode bridge rectifiers I have used, which actually puts two diodes in series. Thanks for clarifying.

 

Sorry I went on so long with that. Got carried away. Hope it was of interest otherwqise!