Hello. Hope this isn't too noob a question, but I am one so it probably is one.

I'm towing a new-to-me 2003 17' Hi-Lo Towlite. I've got 4-way trailer wiring installed on my TV, but the Hi-Lo of course requires 7-way from the TV.

I bought and have (mostly) installed this guy: a 4-way to 7-way adapter from CURT.

The existing 4-way output from the TV goes right into the adapter. Same for my blue brake power wire. And I've grounded the adapter to the TV frame. But the adapter also has a black wire to take aux 12v power from the TV, apart from the 12v that's already a part of the 4-way.

Here's my question: what am I missing if I don't connect this black aux 12v? Will my travel trailer's batteries still charge during towing, or is that part of what I'll be missing?

I'm still trying to digest the electrical systems in the RV. How and when the batteries charge, and from where, etc. All help is appreciated.

Thank you!!

Welcome to the Forum!

You must have the black charge line hooked up to charge the trailer battery. If you don't have a charge line on the tow vehicle now you can run one from the battery using 8 gauge wire with a 30 amp circuit breaker inline back to the harness that is on your adapter.

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There's never a noob question. What year and model of tow vehicle? Some manufacturers have included the 12 volt supply wire in the harness to the back. All you have to do is locate it and connect it to your 7-way and then locate the end in your engine compartment and connect that to your distribution box. Your tv owner's manual should have that information.
If you do have to run a separate wire, I'd suggest buying an aftermarket ammeter from your local auto parts supply house and installing it in your cab in-line with your trailer supply wire. It's a little extra work and wiring, but being able to monitor the charge going to the trailer is worth it.
Welcome to the forum, there's a lot of good information from a lot of good people here.