My 2001 dodge diesel will not hold a charge to the batteries. I replaced the computer and both the batteries. I don't know what else it could be . I hope someone can help?

 

Check for the glove box light or under hood light being on. If you still can't find it, start pulling fuses and check for a current draw to find the circut and trace it from there.

 

See if the charging system really is charging by checking the voltage at the batteries with the truck running. Should be somewhere around 14v plus or minus. If it's down around 12v or so then it probably ain't charging. If it's not charging then check to see if the A/C is working. If the A/C is also not working then you probably have a problem with your Crank Position Sensor.

 

I'm with Heimcat. I have found that a couple of pennies in the gigar lighter can draw current and not pop the fuse. Start pulling fuses and look for a slight spark when you replace it and take it out quick. You'll find the circut, then look at everything in that circut.

BTW, check the lighters!