Bizarre turn signal/headlight issue

Hello Tacoma World peeps,

I recently scored a well-cared for, first gen Taco that is suddenly presenting with a bizarre lighting/electrical issue I was hoping someone may be able to help me diagnose...

So when I got the truck it had a cracked/broken passenger taillight lens--lights and signal all worked as they should but I wanted to replace it with a new one so I ordered one from CARID and swapped it out--the new one did not come with bulbs so I just reused the old ones. Pretty standard swap and everything seemed like it was working properly.

So I'm in the process of getting the truck inspected at a local shop and they discover the issue:

When the headlights or parking lights are OFF--all turn signals work fine, left, right, front and rear. If you turn the headlights or parking lights ON--now the LEFT signals don't work but the right ones still do.

As far as I know, this problem is a direct result of the new rear passenger lens, although I think its weird that driver's signals are the ones that are acting screwy. Since its summer I'm not exactly driving a lot with lights on but I feel like I would have discovered this at some point in the last month. This is soooo frustrating as it's keeping me from getting an inspection sticker! Just trying to avoid the bored cops until I get it squared away

I'm apt to order another lens and see what happens with another one but I wanted to see what the pros here had to say. I can provide more context as necessary but this is gist of the problem.

Thanks in advance for any advice/help!

 

If you think there's something wrong with the lens/sockets/bulbs you could swap them to the other side and see if the problem follows, if it's not that you likely have a wiring or switch issue.

 

Great suggestion--wish I'd thought to do that when I had it apart yesterday I just switched the lens and the problem does continue so I guess it's not a issue with the aftermarket/non-OEM taillight I installed. Bad turn signal/headlight switch the next most likely culprit?

 

Have you double checked your bulb, connector, socket, and wiring?