The rear blinker has been given me grief for a while--doesn't blink. Thought it was bad contact in the socket, but after adjusting them it still happens. Then recently discovered it won't blink if the bulb is fully inserted, but will blink if you hold it in partially. I've tried with the bulb from the other side and same behavior. I made a video, and also hav a picutre of the socket. My guess is the connector on the side has corrosion further down where it typically touches, but is cleaner farther up that makes contact as the bulb is removed. Thoughts? Can that connector be cleaned?

Video of the light bulb being removed

 

Have you got a multimeter? Test the ground, turn the beeper on then put one needle on the ground and one on the frame, although sometimes this doesn’t work. Also check voltage coming in. The terminals look fine, you probably just have a loose connection somewhere and that’s fairly easy to figure out. Test everything, pull on everything, test again, push, again. Familiarize yourself with a multimeter if you haven’t already.

as an aside, several of my terminals are literally submerged in water a lot of the time, and they work. I have a leak in the seal, but it hasn’t caused any problems so I just dump the tail light out now and then.

 

Sounds like the wrong lamp to me.

 

Then bulb that works on the other side has the same behavior on this side and seems to be same bulb type. I'll look more closely to make sure.

 

I verified voltage already, but didn't test ground. Would be surprised if the socket or wiring was bad that it worked correctly halfway out?

 

Are you sure the sockets did not get swapped around, not easy to do but....