My left taillight won't stay on full time. I checked The bulb and also cleaned the connections were the wires attached to the tail light grid.
Bill

 

This sounds like the same problem with every Euro car I've ever had. Typically it is caused by a faulty ground wire. The wiring harness at some location nearby will have a wire that is attached to some kind of bolt directly to the body of the car. This needs cleaning. Often times, the only reason the tail light is on ever is because it is grounding through another hot wire circuit like the turn signal or brake light circuit. But when that circuit is energized, the other circuit dies. So the ground wire needs to be cleaned.

Also, light bulbs are made in China, which means they are crap. There are times when the light filament breaks loose from one pole and flops around inside the bulb. Occasionally it will touch the hot pole where it broke and weld itself back on for a while, only to break loose again later. Take the bulb in your hand and give it a good solid tap with your finger and see if the filament is flopping around in there (or just replace it to be safe).

Finally, check for broken wires or wires chewed by mice. The little guys seem to like eating insulation and can nip wires.

 

I made sure all the bulbs are good along with tightening up the contacts on each bulb to the grid.
I clea

 

I checked all the bulbs,cleaned the contacts all over the grid and for now the left taillight is coming on and staying on when I turn the switch.I also have a taillight converter attached to the wiring with those dumb blue quick connecters,have had it on there for years,I wonder if it's the problem? The converter always works when I hook up my trailer.

 

Converters switch the yellow turn signal to the red turn signal, right? That could certainly do some strange things. The trailer uses the turn and the brake light as the same filament. The car uses separate bulbs, so it has to combine them for the trailer. Not sure what kind of solid-state switch that would be? There has to be some interrupting circuit there with a programmed logic, otherwise your turn signal on the trailer would just go solid when you brake.

The tail light, which is the light that comes on with headlights, isn't involved in that circuit normally, but with additional complexity comes additional possibilities of short circuits. That converter could be a problem.

But still, the grid should have a ground strap. Make sure the part that attaches to the car is good, if you haven't already. Looks like it grounds to the tail light mount stud. Make sure it's super clean. Also, the ground stamp is riveted to the grid circuit board. Make sure it isn't corroded where it attaches to the grid itself.

Those crimp connectors shouldn't cause a problem unless it cut the wire when installing. Consider just wiring up an amber turn signal on your trailer and ditching the converter all together. Intermittent electrical faults are the worst to fix.

 

I made sure all the connections including the ground wire are clean and tight.
I'm considering replacing the taillight converter.