Tag light issue

Thanks Joe for your reply. I thought of that too. Ii can feel the spring in the bottom of the socket as I push in on the bulb and tried pulling and pushing on the center wire with no change. Also I did mention one was a new unit. Also I think if this had been the case they would not have lit up at the battery before installing them. I am now wondering if there is an air space between the inner and outer walls of the socket and the battery at 14 volts was enough to bridge that gap but the voltage drop along the way to the back of the truck is not. I have never cut one of them open and have never seen a cut away view. Another thought I had is there any way the bulb could be creating a direct short back to the socket yet then it should not have passed the battery test if that was the case.

Okay Joe, this is not a factory bumper. This has the single wire tag lights that have been around for years that are suppose to ground when you push them in the hole but when that failed is why I solder a wire to the socket to create a better ground. I was just discussing this with a friend and we thought about running a jumper direct from the battery checking both power and ground as they did work when I battery tested them before installing them. So that will be in the morning and Ii will post my findings. One thing I did not think to mention as it is not a constant issue but sometimes the left turn light on the dash does not come on yet the bulbs are blinking on the outside. Did not know if maybe that is related some how as it is all exterior lighting except for the turn lights in the dash.

This is the style I have, but on mine I have soldered a ground wire to the outside of the socket.

Joe, I live out in the country in Oklahoma. I have three miles of dirt and gravel roads before I reach paved streets. So anytime I need to go anywhere that turns into six miles three going out and three coming home. Plenty of mud puddles and dust. This is not the first set of lights I have had to replace. Usually it is simple I hook the two center wires to the brown wire and take some sandpaper to the hole and pop them in. This time it was already late evening parts stores were closed but my friend had one new one and thought one would be better than chancing running into an officer that was not so understanding. So I did the usual cut one out and used a butt connector to splice it in and sanded the hole and popped it in but I got no light. So I headed home thinking the bumper had lost ground somehow. That was when the idea to add a ground wire came to me so I would not have to rely on such a cheesy ground. So I soldered a wire on and checked continuity to make sure I had a good ground then did a battery test which told me both lights now worked. I have a 4 pin trailer plug that is teed into the rear harness connector instead of the chop job a lot of people do. So I turned on the lights and checked the plug to make sure that it was indeed a source of ground and then tested the brown wire to make sure there was power and there was. So took the center wires to the brown and then followed my trailer plug ground which was hooked to the bumper so knowing that this was already a ground source I hooked the soldered wires up to the same spot. Then turned the lights on but no tag lights so Ii pulled the bulbs and checked center contact to socket and there was 12 volts put the bulbs back in still nothing. Pulled and pushed on the center wire to check for spring tension and slack between bulb and wire everything was tight and still nothing. I went straight from battery test to installation and after confirming there is power and ground to the socket there is no logical reason why this did not work. After breakfast in the morning I will be running the jumper set up and will post the results of that.

Sorry it took so long to get back to you we got hit with a winter storm this morning freezing temperatures and 40 mph wind. Here is what I did and the results Ii built and ran a dual line jumper from the battery to the back of the truck. Made sure they had power meter read 13.81 volts first I cut the ground loose from the bumper and hooked that up and turned the lights on still nothing. Then cut the brown wire and hooked it to the jumper bot tag lights lit up just as they did when I battery tested them before installing them. Then to verify it is a power issue I hooked the ground back to the bumper and both lights lit up. So that eliminates all questions about grounding problem. Before crawling out from under there I checked the brown wire it had 12.37 volts. I still do not get where the problem is one would think that would be enough voltage to run the tag lights. Now the question is, where does the power in the brown wire come from and do I replace the wire or go with the toggle switch plan?

Well for now I went with a toggle switch as long as I remember to turn it on and off which it should not be in a couple of days when I go pick up a lighted toggle switch and swap them out. Thank you your advice was most helpful. At least now I can drive after dark again.