I lose battery charge overnight on my 69 c10. Found out there is a 10 ohm resistance from battery + to ground with key off. This resistance went away when I removed the positive lead from the alternator. I replaced the alternator and have same reading, approximately 10 ohms. Is this possibly a bad regulator? What removes the path to ground through the alternator?
Remove fuses one at a time to find leak. Also brake light if lever type.
Thanks Ed, I pulled all the fuses one at a time and still have leak.
You have a short to ground somewhere or a non-fused circuit that is energized by mistake.
thanks 78buckshot. I have tried to find the short and the only thing I found out is when I remove the b+ wire from the alternator, the short goes away. what would happen if I connected the alternator through the ignition switch instead of straight to battery?
An alternator that draws power when not turning has a bad diode in it.
I would take the alternator off and get it tested.
Fix the problem instead of putting a band aid on it (connecting the alternator through the ignition switch).
Do you have the original equipment alternator with an external regulator, or has the alternator been upgraded to the later internal regulated type? The older system with the external regulator was notorious for diode leaks and the exact symptoms you're describing. I'd recommend trying another alternator before doing anything else. If you choose to isolate the alternator charging wire, don't run the circuit through the ignition switch- - - -use two Bosch-type 60 amp relays wired in parallel and energized by the ignition switch to be able to handle the alternator current without an excessive amount of voltage drop. Even that will be a band-aid fix, however.
Thanks Jerry and Kevin. Good points. Update on my efforts. I have the original equipment with the voltage regulator. When I measure the resistance with the positive lead on the positive post and negative lead to chassis ground, I read approximately 20 ohms. If I reverse the leads the resistance goes way up. I removed the alternator and now I measure around 30K ohms. I pulled all the fuses one at a time with no change. I disconnected the connector to the regulator and the resistance shows an open. Is it normal to have 30K ohms across the regulator. UPDATE went to parts store and ordered new regulator, keeping my fingers crossed.
Unless you have the battery disconnected, trying to measure resistance in a circuit such as the alternator is a lost cause. There is no telling what sort of reading the ohmmeter will give. You might try disconnecting one of the battery cables and using the "amps" function of a digital multimeter to measure the parasitic current draw with all the circuits turned off. It should be no more than a few milliamps. Half an amp (500 milliamps) would be a ridiculously high drain. If disconnecting the big alternator charge lead stops the battery discharge, the alternator is bad- - - -no matter how many alternators you have to swap until you find a good one. You could probably resolve the whole problem by retrofitting to a 10-SI internal regulated alternator and tossing that antiquated original equipment unit into the nearest scrap metal bin. GM's first attempt at an AC charging system was a pretty weak one in the 1960's, and those units haven't improved with age. The newest rebuilt external regulator alternator you can buy will be around 50 years old. You can buy a brand new 10-SI at any corner auto parts store.
I do have the battery disconnected. All my readings were with the negative terminal disconnected from the battery. found a nova conversion kit that will work on my truck to convert to a new style alternator. Hopefully all problems will be solved.
Here is a diagram that is appropriate for the common 10si, internally regulated alternator. Can be hooked up "one-wire," but this is the three wire hookup with "idiot" light, for completeness. The connector for the alternator is available at your FLAPS. If the vehicle wants to run on after the ignition switch is turned off, adding a diode in series with the light will fix that. Summit and others have a low cost diode kit for that purpose, or you can source the diode inexpensively at electronics places.
Update... Thanks to suggestion by Hotrod Lincoln (Jerry) , all battery draining problems solved with the Nova conversion kit and a new style alternator.
"I love it when a plan comes together!" Good work!
Pete, did you "nova" kit come with a wiring diagram? if so, please post it. Thanks.
Nova kit did come with a wiring diagram but I don't know how to post it. If you go to Nova Alternator Conversion kit there is a diagram there.
Take a picture of it and post it according to the instructions up on the left of the page.