Burned 7-way plug contact!

What happened and how to avoid more damage...

Everyone,

Found this post about a 7-way plug with a burned contact on the Cool RV Stuff group. While I don’t know all the circumstances, I can make a few guesses as to how it happened and offer some suggestions. Keeping your 7-way connectors in good shape is important since it’s how your trailer brakes are powered. And that’s a huge safety problem if your e-brakes don’t operate.

I just parked and was putting trailer plug into hitch. Heard an arc and then looked at pins. Never had that happen before. Hooked up to shore power. Is that normal?

Here’s how it’s wired

As you can see from the diagram above, the burned contact in the plug was the 12-Volt Auxiliary Power connection. As you’re probably aware, this is the connection that charges your RV batteries while driving.

I have a few ideas…

This does look like arc damage rather than a continuous overload which would melt the plastic and discolor the brass metal contact. But I’m not exactly sure what caused the arc fault event. However, with modern trailers that have Lithium Batteries and Solar Panels, the voltage at the tailer will be higher than the truck’s engine battery. So there will be a back-feed current which could be significant. Plus this may have been caused by the truck ignition being on while connecting the 7-way plug while shore power was charging the battery. So it’s probably best to connect the 7-way plug with your truck ignition off. More to study…

I see oxidized and loose connections

A close look at the picture shows that the contacts appear to be too wide which will cause to a high-resistance and possible overheating if there’s significant current draw. Plus that can cause intermittent trailer brake operation.

Clean it and protect it!

I highly recommend DeoxIT D5 as the best way to remove oxide from brass contacts. There’s other contact cleaners available at your auto stores, but DeoxIT D5 is simply the best. It only takes a short spray in each contact to remove the oxidation and leave a protecting film that helps prevent future oxidation And don’t forget to clean the truck connector as well.

What about Dielectric Grease?

I think this is a good idea for electrical connections exposed to the elements. While it’s not actually conductive, Dielectric Grease does protect brass contacts from oxidation due to moisture. And the contact pressure pushes the grease away from the actual connection which allows the electricity to flow. But you only need a little bit, so a toothpick is probably a good applicator. Once again, apply this sparingly to your truck’s 7-way connector after cleaning it with something like DeoxIT.

Should you bend the connectors to tighten them?

While I don’t recommend just bending connectors randomly, you can see in the first picture that there’s a lot of gap between the brass contacts, which will contribute to high-resistance connections which might fail when you need something important to work (like trailer brakes). So a small screwdriver used to carefully close the contacts is okay, but don’t go crazy bending contacts, and if they won’t stay tight then the 7-way plug should probably be replaced.

More on this next month

I’m teaching an interactive online webinar for RV technicians next month on maintaining 7-way plug connections and testing trailer brakes. I’ll be able to post that info in a future newsletter, and I could even do a live-streamed video for this group if you like. Please let me know.

Let’s play safe out there…. Mike