I've replaced the battery and the altanator

ive replaced the battery and the altanator

If you've verified power and ground as well as continuity in the harness, there's still an external voltage regulator (mounted under center of dash panel) that could be your problem.

. Check all under hood fuses with a test light or multimeter, especially any "mega fuse" where the alternator "B" wire attaches to the fuse box.

. Install a new voltage regulator, being sure to create a "soft" spark to establish polarity. Follow the directions explicitly that come with the new regulator; otherwise, the new regulator won't work.