(Hey guys, first post here) anyway, bought a 2002 ranger last week. 2.3, 2wd. Ran great for a day, then the clutch, alternator, that rediculous disconnect for the slave wore out and wouldn't stay in, all in a week. Got all that sorted out but here's where I'm really stumped. When I jumped the truck after I replaced the alternator, it started up fine. The second I pull the cables off, it dies, but i still have power in the cab. Not enough to start it, as everything goes dim and I hear the starter click. I figured the battery was shot, but last night the interior lights came on and wouldn't shut off. Like the door was open but it wasn't. And the switch on the dash is off. Also, now my speedo is jumping around 15 mph and my odometer is climbing as well. Is that related to the dead battery, if it really is toast, or do I have a wiring issue somewhere? Any help is greatly appreciated at this point. I've put 25 miles on it since I've bought it. Starting to get aggravated with it.

 

Just FYI, you should avoid jump starting 2000 and up vehicles, especially with another 2000 and up vehicle, you can damage both.
If you do need to jump start, there are two ways
Remove your battery cables and let other vehicle charge your battery, then remove jumper cable and connect battery back up to start.
Or shut off other vehicle disconnect its battery cables and use unhooked battery to jump.

It reads like strictly a battery issue.

You need a volt meter, set it to DC volts
Check your battery voltage, 12.3v to 12.8v is good battery, below 12.2v is discharged or bad battery, unhook cables and charge it.

Once engine is started battery voltage should read 13.6 to 14.8volts
If it still reads 12.2-12.8v then alternator is not providing power, there are fuses in engine fuse box labelled Alt, check them.
2002 ranger 2.3l also shows Fusible Links for alternator power, these are short Brown and Gray wires, 4"-6" long, and are used as Slow Blow fuses, they will separate if AMPs get too high, which can happen when you jump start, it also blows fuses.

Anyway disconnect your battery for at least 5 minutes, after that time touch the two battery cables together, this will discharge any capacitors that still have power, and this will clear any glitches in the system from low power, basically a Reboot of the system.
Once your battery is charged up reconnect cables and try to start engine, then check alternator power as described above.

Working alternator will provide close to 15v just after starting engine, this is to recharge battery from starting, then after a few minutes voltage should start to drop to 13.6volts, this is a maintenance charge, it keeps battery from draining and is a low enough voltage not to "boil off" chemicals in battery.

Battery's last from 5 to 8 years, usual battery failure is a build up between the plates inside, a short between plates will cause battery to self drain, so battery will start engine if it only sits less than 6 hours, but if it sits 10 hours it can't start engine because it has drained too much