I guess the first question to ask would be: Do you have a round 7-pin "Bargman" type trailer plug? To run a charging circuit you will need one if you don't already have one installed.
Wiring Code 7 way Car End # Color Gauge Circuit Function connector interior
1 white 10 ga. common ground
2 blue 12 ga. electric brake
3 green 14 ga. tail/running
lights
4 black 10 ga. battery charge (+)
5 red 14 ga. left turn/stop
6 brown 14 ga. right turn/stop
7 yellow 14 ga. auxiliary/back up
Note on pin #7: Please note that the center terminal is labeled as an auxiliary circuit, most commonly used for backup
lights, and
is not a ground terminal as many try to make it.
Wiring Code 7 way Trailer End # Color Gauge Circuit Function connector interior
1 white 10 ga. common ground
2 blue 12 ga. electric brake
3 green 14 ga. tail/running
lights
4 black 10 ga. battery charge (+)
5 red 14 ga. left turn/stop
6 brown 14 ga. right turn/stop
7 yellow 14 ga. auxiliary/back up
Note on pin #7: Please note that the center terminal is labeled as an auxiliary circuit, most commonly used for backup lights, and
is not a ground terminal as many try to make it.
This chart should be used as a general guide only, you should always test before connecting your wiring.
This chart also may not be accurate for vehicles with factory installed trailer harnesses. In past 2-3 years manufacturers have begun to match the wire colors to the code for the common 7 way RV connector.
As a precaution, if your vehicle is equipped with a diagnostic indicator that tells you when a lamp is burned out or not functioning, you may need special wiring adapters and testers. Not using these adapters may cause damage to the vehicle wiring or computer.
In addition to the above some cars and trucks have a separate
light for the brake
light, most commonly identified by amber turn lenses in the rear. If you have this type of wiring a converter is required.
I recommend attaching the trailer harness ground directly to the frame or a solidly attached sheet metal part, using a screw or bolt. The single most common cause of trailer
lighting problems is a poor ground on the tow vehicle or trailer.
the terminal.
Hope this helps.