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Hello, I have a 1999 F250 Super Duty 7.3. I went out to start my truck and its completely dead, no lights nothing. I took the batteries out and checked them. They are completely dead. I bought new batteries, installed them, tested the alternator and battery both read in good range. Truck started and ran fine. Next morning came out and the battery is completely drained, no lights anything. Any recommendations on what may be doing this? thanks
You say the alternator checks out? Check it for heat after you charge the batteries. Disconnect them for charging so they're not discharging as they try to charge. Parasitic drains can be hard to track but it sounds like yours is a major drain and shouldn't be too bad if you troubleshoot it properly.
A friend had this issue, and he hunted and hunted but could never find the drain. He broke down and would disconnect the batteries at the end of the day.
One day when we were working on this truck- installing a power inverter. we were under the driver seat and accidentally touch the motor of the power seat. It was burning hot!
It had froze up and was constantly drawing power. We disconnected it, and the problem was solved.
Run through the draw test procedure Sous linked, should lead you right to the problem circuit fairly easily. I'd suspect it's a significant draw or more than one to drain 2 new batteries in less than 24 hrs.