The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - 55.2-59 Battery draining

leegreen · 06-23-2023, 09:58 AM

>draws 4v when the plugs containing the 2 small wires is removed but the wire going between the alternator and battery is still connected.

This sounds like alternator problem. does it go to zero when all the wires are disconnected from alternator?
Yes -> leave alternator fully disconnected and use some other piece of wire to bridge from battery to the main terminal on alternator, if you still get 4v I think the problem causing the low voltage leak is inside alternator, if the problem goes away there is a short in that main cable to ground.
No -> there is another leak somewhere with high resistance, unplug more stuff until you see the voltage go to zero - start with ignition switch

The larger leak when either red or white wire is connected:
the white exciter wire problem is either the ignition switch or you do need to add a diode to stop back feed of power from alternator to ignition. Does wiring kit instructions say anything about diodes? White wire basically turns the alternator on with ingition.

The red wire, where does the other end go to? Red wire should be live only when ignition is on, its purpose is to let the alternator see the voltage of the system from somewhere away from the battery to adjust for any voltage drop due to the loads. Usually goes to somewhere near fuse box. without it, the alternator may overcharge, if it connects too close to the battery and there is voltage drop in the system some parts of the truck may be getting too few volts.

Fuse box will always have some power: horn lights and brakes at least will always have power. other fuses will only be hot when the ignition is on.

a test light like this is my goto for finding out what has voltage and what does not. get them anywhere for a few bucks
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Views: 3293
Size: 16.9 KB

Also very handy is a few wires with jumper connectors on each ends so you can hook stuff up temporarily to see if it works. I made up a pair of truck length jumper wires from some old speaker wire, it has been very useful for testing on several car and boat projects we have going on.

ps: I edited the yes/no paragraph a couple hours after the original post as what I wrote earlier did not look right after a cup of coffee.

06-23-2023, 09:58 AM	#33
leegreen Registered User Join Date: Mar 2022 Location: Surrey BC Posts: 983	Re: Battery draining >draws 4v when the plugs containing the 2 small wires is removed but the wire going between the alternator and battery is still connected. This sounds like alternator problem. does it go to zero when all the wires are disconnected from alternator? Yes -> leave alternator fully disconnected and use some other piece of wire to bridge from battery to the main terminal on alternator, if you still get 4v I think the problem causing the low voltage leak is inside alternator, if the problem goes away there is a short in that main cable to ground. No -> there is another leak somewhere with high resistance, unplug more stuff until you see the voltage go to zero - start with ignition switch The larger leak when either red or white wire is connected: the white exciter wire problem is either the ignition switch or you do need to add a diode to stop back feed of power from alternator to ignition. Does wiring kit instructions say anything about diodes? White wire basically turns the alternator on with ingition. The red wire, where does the other end go to? Red wire should be live only when ignition is on, its purpose is to let the alternator see the voltage of the system from somewhere away from the battery to adjust for any voltage drop due to the loads. Usually goes to somewhere near fuse box. without it, the alternator may overcharge, if it connects too close to the battery and there is voltage drop in the system some parts of the truck may be getting too few volts. Fuse box will always have some power: horn lights and brakes at least will always have power. other fuses will only be hot when the ignition is on. a test light like this is my goto for finding out what has voltage and what does not. get them anywhere for a few bucks Also very handy is a few wires with jumper connectors on each ends so you can hook stuff up temporarily to see if it works. I made up a pair of truck length jumper wires from some old speaker wire, it has been very useful for testing on several car and boat projects we have going on. ps: I edited the yes/no paragraph a couple hours after the original post as what I wrote earlier did not look right after a cup of coffee. Last edited by leegreen; 06-23-2023 at 12:26 PM.