Weird alternator reading on the gauge

[Speakrdude]

On my port engine, the alternator gauge dances around at certain RPMs. The slower the higher the voltage, the faster the RMS, the dancing begins, then lower reading.
​Could be something as simple as the two smaller wires on the alternator (not the +12 orange, and not the gnd.) being swapped? I replaced recently and they were hard to tell the colors, due to paint.

(See video)

 

[alldodge]

As always, it is very important to know what we are working on serial number is best, at least 4, 6 8 cyl and year

I replaced recently and they were hard to tell the colors, due to paint.

I would start by taking a meter and place it on the ALT output terminal. If the ALT is doing the same thing check those wires. Guessing you have a Mando ALT

Tried to post a pic but appears iboats is having an issue right now. Back of ALT wire on left is purple, one on right is red/purple

 

[Fun Times]

Slipping belt could allow that to happen, bad/corroded/loose wire connection/s as well and yes those two wires you mention swapped incorrectly could do that or an internally bad alternator are all things to consider checking too.