86 gmc 2500 electrical

[ssgtnelson]

hey I cant seem to keep a charge in my battery. I have replaced the alternator and the battery itself and have gone over all the ground connections and they seem to be in order. I need some help

[bradrhale]

seems as if you have a something draining your battery. with everything turned off, go one circuit at a time until you find something drawing power. i hate electrical work.

[ssgtnelson]

yeah me too... should I work from the circuit panel or from some other spot?

[bradrhale]

fuse box is fine. good place to start. if nothing there, might have to dig a little deeper as it might be a contactor that is fried and is grounding. have you noticed anything staying on or acting up and not functioning??

[CharlyG]

If it is draining in a short time, you could just unhook the pos side and notice the size of the spark when you touch the pos to its terminal. If it takes overnight to drain, this won't be a good test, but if you have a huge drain, you will see a corresponding huge spark! Just a dumb shade tree trick I used to do.

[ssgtnelson]

well the thing is it doesnt drain when the truck is off but it wont recharge while its running so every time I start it i lose some juice and i get left at the most inconvenient spots

[bradrhale]

when you replaced the alternator, did you have it tested?? have you thought about testing this new one?? make sure your plugs are connected good and cleanup all your ground connections to make sure you are getting a good ground.

[Chevy_Finatic79]

do you have access to a multimeter?

**WITH THE VEHICLE OFF**
set the meter to read AMPs

1. Remove the negative side battery cable from the negative battery terminal.
2. Attach an ammeter(this measures amperage) between the negative cable and the negative battery post. wait a few seconds to several minutes for the car to go into sleep mode. i.e. when you make the contact with the test light the cars computer systems "wake up" after a bit of time they will go to "sleep".
3. If the ammeter is reading over 25-50 milliamps, something is using too much battery power.
4. Go to the fuse panel(s) and remove fuses, one at a time. Pull the main fuses (higher amp ratings)last.
5. Watch for the ammeter to drop to acceptable drain. The fuse that reduces the drain is the draw. Consult the owners' manual or service manual to find what circuits are on that fuse.
6. Check each device (circuit) on that fuse. Stop each lamp, heater, etc. to find the drain.
7. Repeat steps 1&2 to test your repair. The ammeter will tell you exact numbers.

EDITERS NOTE: The original author listed this repair using a 12v test light. As an ASE certified mechanic, the best place for your test light is the trash. A test light doesnt measure voltage; it shows if enough voltage is present to light the lamp.

1. An ammeter meaures current (in amps), and that is what you are fighting against if you have a parasitic drain problem.
2. Harbor freight sells a $3 digital multimeter (dmm) that has an amps setting. I use a Fluke, but it's whatever your trying to spend your dollars on.

[edit] Tips

• A parasitic drain is when an electrical device is using battery power when the car is closed, and the ignition key removed. Therefore, when doing this test make sure that the dome light, under hood light, trunk light, etc. are off.

[edit] Warnings

• Don't forget to check inside cigarette lighter and power sockets. Sometimes coins can fall in and cause shorts.
• Some after-market alarm systems may make this test too long or loud to be worth the effort. If that's the case, seek professional help.
• Be careful working around the battery in a car.

[leolkfrm]

I suspect its a rebuilt, take the alternator back to where you bought it and exchange it. Tell them its not charging as it should, probably a bad regulater