My battery keeps dying. Its only a couple months old. I think its good cause if i charge it and leave it disconnected it stays charged. something in my truck is draining it. where do i start? I have made sure to have all the lights of radio off . My truck is a 93 F-150 4x4 XL.
How long does it take to run down? First take the battery to an auto store and have it tested. If it only take a few hours, I would charge the battery and pull 1 (ONE) fuse (i.e. radio, brake lights) and see if it stops the problem. It will take time to go through all of the fuses. If none are found it would be in the charging system.
I had this problem when my alternator went out. Let the thing sit and it was done, dead, etc. It's really easy to pop the Alternator out, too, so you can figure if that's the problem or not. Get under the hood, loosen the idler pully, unbolt two bolts on the alternator, and the thing comes free. Then take it to your auto store of choice and have it tested. Doesn't take long at all. If its the Alternator then, depending on the shop, they might be able to replace a failed peice, or youcan of course get a new one/remanufactured one. If you do have to get a new/reman one, take it out of hte box and compare it to the old one. I went to two places before a third informed me that I simply needed the alternator to be 'clocked' because the wiring wouldn't line up right. Oh..and just for peace of mind, get a lifetime warranty one. Kinda like insurance, except this one isn't unfair and female biased. ^_^
If its not the alternator, happy hunting in the fuse box. My grandpa had a fuel relay or something drain the battery on this truck once...he said he bashed the fuse box and it learned its lesson. If it hasn't adversly effected anything after 5 or 6 years, then alls good I suppose.
Best way to isolate the drain is to pull the ground cable and hook it back up thru a multimeter with a DC amperage check function [even cheap $10 meters have it]. This way you can see how much curent is being drained, then disconnect bits or pull fuses till the flow stops. Start with the radio/clock fuse as that's an automatic trickle, what's left [if anything] shoud be your mystery drain. Have someone watch the meter while you pull fuses.
Similar to 83Van, buy a test light for $1.99, late in the day before dark disconnect the negative terminal, connect the little clip to the cable terminal, touch the point of the test light to the negative post. You now have a light wired in the circuit. If there's any current flowing, the light will glow, maybe quite dimly. Test it by leaving the door open with the dome light burning...you'll see. A clock won't even make it glow.
If you don't get a glow, you have no short....maybe the battery has a dead cell.
If you do get a glow, pull one fuse at a time til it stops glowing. Then maybe pull one bulb. I once had a bad diode in the alternator that made it glow, pulling the fuses didn't help me find it.
Good luck. This procedure will help you the rest of your life...pass it on.
Thanks for the replies. I tried the bulb method and the bulb glowed the same no matter what fuse I pulled. I will try the DC amp check tomarrow. The battery is only a few months old and the alternator is less than a year. The alternator while the truck is running will put out something like 14.5vdc. With the truck off i have 12.5vdc on the battery. The next morning the battery voltage will be 9 or 10 vdc.
If you've pulled every fuse and still have a drain I'd suspect something in the charging system, mainly the voltage regulator and the alternator. If you have an external voltage regulator start there, repeat the same drain test but with its harness unplugged. If the drain is still there do the same with the alternator, will just be a bit more work getting to the wires.
If something goes bad in the charging system [usually a diode], then the battery can start back feeding the alternator.
You can replace just the regulator. Its just a matter of pulling off the back and removing and replacing. You will have to make sure the brushes stay in when you replace it. I used to use a straightened paperclip to hold them until the regulator was screwed in place.
(Thats if it has the internal regulator, either way, the answer is you can just change it without changing the alternator)