Tail light glows when 7-pin is wet

Rick24 · July 1

My taillight glows when my 7-pin connector is wet. Is this a problem? What causes this?

SLJ · July 2

When it's wet the 12 volt battery pin in the connector can send current to the pin for the taillights. Dry the contacts. make sure the connector is facing down when unplugged or put it in a plastic bag to keep it dry.

Bayliss · July 2

@Rick24, I agree with @SLJ.

Water on the seven-way electrical contacts can cause current to cross the metal contacts, creating an electrical short. Dry the contacts (e.g., with a hair dryer) and then spray some electrical contact cleaner (e.g., CRC “QD Electronic Cleaner”) on the seven-way receptacle and plug contacts. Allow the cleaner to dry and follow-up by adding a thin coat of dielectric grease to the contacts to improve the electrical connections and help repel water intrusion. (NOTE: by only applying a small amount of dielectric grease, such as with a toothpick, the pressure of the metal contacts coming together will push the dielectric grease away, thus maintaining electrical conductivity while also repelling moisture intrusion.)

Here's a video that provides some info on cleaning the seven-way plug and receptacle:

https://www.youtube.com/watch?v=H6occ6I_6HU

Most likely, in the scenario you have described, water is creating an electrical bridge/contact between the 12V+ pin and the tail lights pin (see photo below of the seven-way plug):

Image: https://us.v-cdn.net/5021717/uploads/editor/ed/llv119gli1pr.jpg

donmontalvo · July 2

I could be wrong, but I believe dielectric grease will prevent arcs and shorts from moisture, but need to clean the contacts to improve the electrical connections.

WayneW · July 2

All spot on advice. I always thought dielectric grease would help with conductivity. Heck, it’s got electric in the name. But it turns out dielectric grease is nonconductive. It does a great job at sealing out moisture and preventing corrosion, so it does help maintain conductivity, but the connections do need to be corrosion-free to start with. Seems like they could have come up with a better name.

There are some pretty neat 7-pin protectors that are kind of like an upside down little cup. You push the 7-pin connector up into that and a clip holds it in place, keeping it protected from any moisture. I’d just be wary about drilling into the frame to mount one of those. I just point the 7-pin connector down when not connected, as @SLJ recommended.

Sharon_is_SAM · July 3

TABNewbies · July 3

We fitted one of these 'upside down cups' 4 years ago and been great - has its own zip ties onto the jack and easy to install. And somewhere to hold the plug anyway and keep it off the ground when not in use.

Image: https://us.v-cdn.net/5021717/uploads/editor/27/yj3dkzsnxnf2.png

https://www.amazon.com/HUSKY-TOWING-81497-Connector-Storage/

tabiphile · July 4

All good and an opportunity to remind that dielectric grease should never be used on contacts, inside of a connector, in your sparkplug boots or anywhere else where current is supposed to flow. Use it to shield connectors from water incursion.
Connectors, by design, are intended to function "dry". The materials that they are made from, as well as any plating that is present, is intended to maximize current flow. The design is intended to cause a form of abrasion between male and female when the contacts are exercised. That scraping is intended to improve current flow. Connector contact design is a very precise and specific engineering practice. Introducing a resistor (dielectric grease) interferes with the operation of the connector. Water can result in shorts between contacts, so keeping water out of the connectors is essential. Use covers, dielectric grease, careful storage to keep water out.

donmontalvo · July 4

tabiphile said:

...[snip]...dielectric grease should never be used on contacts...[snip]...

I had issues with my 7 pin connector, turned out the pins were corroded and loose.

I used a brass brush to scrub the pins, tightened them, then applied dielectric grease (yes even on the connectors).

From that point forward, the 7 pin connection has been 100% reliable.

IMO dielectric grease won't interfere with a 7 pin connection, unless the pins are corroded/loose.

tabiphile · July 4

donmontalvo said:

tabiphile said:

...[snip]...dielectric grease should never be used on contacts...[snip]...

I had issues with my 7 pin connector, turned out the pins were corroded and loose.

I used a brass brush to scrub the pins, tightened them, then applied dielectric grease (yes even on the connectors).

From that point forward, the 7 pin connection has been 100% reliable.

IMO dielectric grease won't interfere with a 7 pin connection, unless the pins are corroded/loose.

Hmmmm.....ChatGPT trumps 45 years of industry experience including directly with Molex, Amp, T&B , Amphenol etc. engineering. Never saw that coming.
Your problem was corrected by removing the corrosion and tightening up the connector. By design, connectors need an interference contact to work properly. Putting dielectric grease into the contacts did not correct the problem, although with an already damaged one, it may be preventing reoccurrence, currently (intentional) your connector is holding on with its nails and will fail again. The ChatGPT summary does correctly conclude that the grease should "not be used to conduct, only around the connection points."

lino · July 5

Using a cap is always helpful. We’ve been doing it on both of our trailers from the beginning. Cheap and easy

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Tail light glows when 7-pin is wet

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