Trailer wiring - 7 Way


New member
eTrailers suggest this wiring diagram for a brake controller. It appears that a solenoid switch is ALSO needed in the black Hot Lead just after the 40 Amp circuit breaker.

The solenoid will presumably prevent the trailer's accessories from draining the Jeep's battery.

Is that correct?




Well-known member
Premium Member
That's a good idea. It totally sucks when you park at night and the Tow rig battery is as dead as the trailer battery because someone forgot to turn out the lights or turn off the furnace.


Premium Member
Unless you plan on leaving the trailer hooked to the Jeep while camping, you shouldn't have to worry about the trailer draining the Jeeps battery.

And, if you do leave the trailer hooked, just unplug the wires.

4x Adventurer

New member
I don't see a solenoid in that schematic? I can't say I've ever seen a solenoid wired as you've described. I do like the use of automatic circuit breakers rather than fuses. Unless I just make a quick stop for the night, I always unplug the trailer from the truck. You have to run a LOT of stuff to drain a deep cycle RV battery and the truck battery in 8 hours. Figure out the drain from everything in your trailer and compare that to the output of the RV battery. Remember the battery amp/hour output changes with amp draw. Meaning that the draw at 10 amps isn't half the time as drawing at 5 amps.


Make sure you use a constant duty solenoid, a regular starter solenoid is not designed to be on for extended lengths of time.

Shawn Trooper

Active member
I've done countless installs with the use of a blocking diode. Part number T85HFL40S02 is a good candidate for this function.