Tail light issue

Experiencing issues with the driver side (left) tail light circuit board. The brake bulb, left turn signal bulb, and reverse indicator bulb are not working. Both the top and bottom running light(s) bulbs are working when activated. However, when the left turn signal and/or hazard lights are activated, instead of the left turn signal bulb turning on, both the top and bottom running lights flash in sync with the turn signals. Tonight I am going to temporarily swap the driver and passenger side tail light circuit boards to see what happens. Any ideas on where the issue might be? Vehicle electronics is not my strong suit. Any suggestions and/or advice would be greatly appreciated! It is my understanding that tail light electrical issues with GM Mini vans from this same generation are quite common.