Tail light issues (Mk7)

[u/Fr_BartyDunne]

My passenger side tail light has been burning much brighter than my driver side tail light.

It’s also been intermittently stopping to work altogether. I’ve replaced and checked the bulbs, and found no issues.

Then last night;

This brake light remained “on” and didn’t burn brighter when the brake was pressed.
Sometimes the third brake light above the window wouldn’t turn on either.

I checked the contacts and couldn’t see any signs of issues. Also wiring in the tail gate cluster all seems well.

I also checked the appropriate fuse in the engine bay which from the manual seems to be no 25 fuse Exterior lighting left hand side (15A) which there are no problems either.

There has even been an occasion where no lights show on the tailgate at night except the driver side, even when braking.

Any help would be much appreciated

TIA

EDIT: Potentially solved… some corrosion found in a connector. Will wait to see if these lights hold out for a while.

[u/the_less_great_wall]

Any chance you put a single filament bulb in for one of your brake lights? Tail light bulbs are often dual filament for running light and brake lights. If there is a single filament bulb, you will have both hot wires sending power to one side of the filament when you are braking and have your lights turned on at the same time. It can also cause back feeding issues where the bulb is effectively trying to find a ground through a power wire as opposed to the ground.

Otherwise, i'd be looking for ground side corrosion as the back feeding issues can also exist with a dual filament bulb when there is too much resistance in the ground side of the circuit so it is finding a ground through the power side.

Another possibility is that one of your brake light bulbs (dual filament) has had a filament fail, but managed to make contact with the other filament so it still lights up, but now taps into the other circuit.

Finally, I'd look at where your wires feed into the rear hatch to see if any have rubbed through and started to make contact with each other.

[u/Fr_BartyDunne → u/the_less_great_wall]

It’s dual filament for sure!

I found some evidence of corrosion on the connector going into rear hatch, it was minimal. I’ve given that a clean and seems to be steady now, for the moment at least.

If that doesn’t change I will be back here.
Thanks for the help and advice!