06 Pete Charging System problem

Hey all,

Got a quick question regarding the chargin system on our tractor seems like the alternator's going out on it but not completely sure weather it's the alternator or the gauge. Dad left the sleeper light on all night last week and drained the batteries. Climbed in the next day managed to get it fired up gauge read 14 volts let it idle at 1000 for about 25 minutes to recharge the batteries and shut it off. climbed in it today to run it up to shop out of town to get some welding done on the trailer and only had 12 volts. Had a dump valve wired into the tractor earlier this week but don't think that would have anything to do with an alternator going out. All the battery posts are good all the connections are alright (alternator and battery) but still only have 12 volts. The alternator only has about 20,000 miles on it and it was brand new when it was put on so it's got me scratching my head a little. I'm no mechanic but leaving a sleeper light on all night shouldn't have shorted something least you wouldn't think and wiring a dump valve in shouldn't have caused the problem either. Just wondering if ya'll have any ideas. also it'll hold steady at 12. It was chilly this morning and it cranked a little slow at first but when I came back to pick the trailer up it fired right up so it would appear as though the alternator is still charging i had every light on for 1 1/2 hours on the way up. Any ideas would be helpful.

thanks

 

Thanks for the info I'll remember that if it ever happens again.