Buddys truck 03/04 F250 6.0. Mostly stock. He cranked it up and noticed it took just a little longer than normal and then he turned his lights on and they were dimmerr than normal. He figured it just drained a little while cranking it and took off. Closer he got home the worse it got. Long story short he (by a miracle) made it home with no lights,gauges,radio, brake warnings etc... Not sure what even kept it running. He disconnected both batteries charged them up. Tested out good and the alternator tested out good. He took it and dropped it off at the dealer, told them what happened and what he did. They have had it a week and can not find any thing wrong

Any one had some thing similar to this and can tell me what to tell him to check.Thanks