Turn signals only work with my headlights off

We need to start with checking the power coming from the BCM when the turn signals are on.

https://www.2carpros.com/articles/how-to-check-wiring

Basically, the BCM needs to send the signal and if the headlights are on, I suspect we have a wiring issue or possibly even a BCM issue.

So, I would suggest we start with checking the voltage and we need to check for codes.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Lastly, can you get me the part numbers of the headlights that you installed? It is possible that if we got the wrong assemblies that this is an issue as well.

Thanks