Check your wiring harness, follow the wires from the bumper back forward, or use an ohm meter to check for continuity. Search on YT for videos on trailer wiring, or go onto an rv forum and go to the towing threads/section then search. Consider adding a separate charge line that is properly sized and fused.
The 3 examples below don't directly address your "hot smell" but you get the idea...
Examples:
fiberglassrv.comforum, 5-28-2020
"If you don't want to mess with your existing wiring, the easiest way would probably be to add a second connector between car and trailer. To make sure you have enough capacity, run a 10 gauge wire (black or red) from your
car battery positive to the back of the car. Connect another (white) wire to a convenient chassis point near the rear of the car (or run all the way from the battery) for the negative. Run another black (or red) and white pair from the trailer battery long enough to reach the car. The positive wire should have a 30 amp fuse at the trailer battery. Affix an Anderson or similar polarized pair of plugs at the connection point.
To be sure you don't discharge the
car battery while camping, either unplug your new charging wire when camped or use a relay between the car battery and the trailer. If you're electrically knowledgeable and have easy access to to a signal voltage to turn the relay on only when the car is running, you can wire it that way. Or you can spend more and use an easy to wire inline voltage sensing relay. Good luck with your project."
(IRV2 forum) 5-16-2021
As sirtate points out the 7-pin plug will have a 12v charge pin. My experience has been that it can keep your battery topped off under light to moderate loads but may not do much in terms of recharging a more deeply discharged battery. If you don't think you are getting any charging at all I would check to see if a fuse needs installed on the tow vehicle - sometimes the fuse is not installed from the factory so the charge line is dead.
I think for a lot of folks the basic 7-pin plug is probably sufficient. If you need, or want a bit more capability than that a DC-DC charger would be the way to go.
I added a new wire run using 2 gauge wire through an 85amp continuous duty ignition-switched solenoid to run through a Victron Energy 30amp DC-DC charger. It's connected to a second umbilical coming from the trailer using an Anderson Powerpole connector. I've seen it push close to 40amps to my pair of 6v GC2's. One of the nice things with the DC-DC charger is the ability to use either a pre-defined charge profile (FLA, AGM/GEL, Lithium, etc.) or create a custom profile which is what I did based on Trojan's recommended charge values for the T-125's. It also allows for the correct, constant voltage needed for the specific charge stage its in.
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TT: 2019 ORV Timber Ridge 23DBS, Blue Ox SwayPro 15K/1500
TV: 2019 Ford F-250 XLT SuperCab LB, 6.2L, 4.30/e-locker, 4x4, 164" WB, RoadActive Suspension
