My 6 year old trailer's rear lights are very dim. You can hardly tell that the blinkers are on during the day. What the best way to tackle this? I assume I need to make sure the currect voltage is coming out of the tow vehicle plug. Yes? Then what? Thanks in advance.

BWT, the side lights seem to be fine. Has anyone replaced their rear lights with LED-based lights?

Rich,

It's likely a corroded common ground connection considering more than one light is dim. It might behoove you to take all the ground connections apart and clean them up then re-attach securely.

Good luck with it, ya gotta have good lights.

Likely corroded ground connections. Turn lights off, remove the tail light lens and without touching the bulb, loosen the screw that holds the ground wire to the RV body. Then move the ground wire, retighten the screw, and turn the lights on. That should ensure ground is good. If there's no body screw for the ground, perhaps the wire connection (crimped StaKon) has corroded inside...
Obviously you should see the same voltage at the trailer plug as you'd see at the tail lights. -Should be around 12.5 vdc, but could be as high as 14.2 vdc depending if the TV alternator was charging.

That is probably the root of the problem..but I have found that the tail light lens and the reflectory surface inside the tail lite get very dirty and dusty..this in itself will cut down on brightness..I cleaned mine out and then using silver enamel touched up the surface behind the light bulb, it made a big difference..make sure you dont paint any connections over or it will ground out and short everything out..

Thanks for the great suggestions. They have never been terribly bright (the lights, not me ) and I don't know if they have gotten worse or I'm just noticing it more.

Has anyone ever replaced their bulbs with LED fixtures? I sure like the way they look on the back of trucks.

Another vote for poor ground. The trailer plug is the most common culprit. Clean all connections with a fine abrasive like baking soda, a pencil eraser if the contact is large enough, or spray can electrical contact cleaner if its in a tight place. Some trailers ground each light to the metal skin and depend on metal-to-metal somewhere to make contact. Better manufacturer's use a separate ground wire alongside the hot wire to each light. The truck plug wiring is another source of poor ground. When installing the plug, some aftermarket installers run the ground wire from the plug to the nearest metal. The best option is a separate ground wire from the plug to tow vehicle battery.
On a different note, the lights are a source of water entry into your RV. The light base is usually sealed onto the RV, but the wire entry hole is wide open. If the lens fills with water it can flow through the wire openings directly into the walls. One solution is drill a small drain hole (1/16") in the bottom of each lens.

camper1b the led lites are very good but a bit pricey. Some truck stops carry them and I believe camper world might. You will still need a good ground but the advantages are quicker illumination with less current and increased longevity.