2013 Raptor 125000 miles. Left taillight went out. Tried cheap LEDs from Amazon and they didn’t work (of course) even with built-in resistor. Switched back to OEM halogens and now nothing works on driver’s side tail lamp - parking, brake, turn signal.

Backup lights on both sides don’t work though I suspect they didn’t work before the current problems on left side.

Front left and mirror blinker work on rapid-blink.

I tested ground by probing bulb connector and touching to frame. Seems ok but I’m not convinced because the rear running and license plates lights occasionally flicker. I’ll remove and clean the ground-to-frame connections just because.

My trailer running aren’t working either brake and turn do work) the last time I had a trailer on. I noticed a wire pulled loose from the rear of the trailer connector but haven’t dealt with that yet. I tried disconnecting the trailer loom from the frame connector just above and at rear of spare tire. Now my rear parking sensors aren’t working. Ugh.

All fuses are good.

So I need so ideas on how to diagnose why the left rear taillight isn’t working. And the backup lights and now the parking sensors. Thanks.