Battery Light?

[Ford67ranger]

Just got a 00 F250

1 of 2 batteries tested bad, so I replaced both
Battery light was flickering so I replaced the alternator (with a reman, lifetime warranty).
Light came back on after alternator replacement, took it back to Autozone and it checked fine.
All grounds are solid and so are the hot wires.

So it seems like I have traced the problem to the 2 wires between the back of the alternator and the gauge. Anyone have this problem? I've heard you can replace the plug.