99 ram 2500. torque converter locking & unlocking constantly only when i have my lights on. As long as lights are off everything works fine. Any advice on where to start looking would be greatly appreciated.

Start with checking stray AC voltage out put from alternator.

 

 Then think about doing this.

 

Yea... It's an alternator problem for sure. 

Sounds like an an alternator on its way out. I would also vDrop test the ground cables as well and make sure that both are close and or passing.

Mine was doing this too in humidity with the headlights on. The drivers side ground cable was borderline failing for me. and that was the root cause of the lock up issues for me. After replacing all of the battery cables (I did them as a precaution), I haven't had an issue since.