I have a 99.5 F350 SD 4wd CC DRW 7.3 ltr. The head lights and interior lights dim and the battery light flahes at the same time. Doesn't do it all the time, seems to follow bumps a lot. Sometimes you might go 50-100 miles without any problems. Volt meter readings on both bats and alternator read 14.8 to15.1 range everytime I've checked and I have checked multiple times. Now I'm leaning towards ground problems. The two ground wires bolted to the frame under the bed are tight, otherwise I haven't followed the ground wiring yet. Any ideas??? Thanks for any help, Luke

 

Look for a loose wire with a cover over it (like on the alternator).