Switched reverse lights

[FF_PM]

I am going to add LED reverse (under trailer and bumper)lights, powered from the RV, switched through a relay from the tow vehicle 7 pin. This will turn the reverse lights on when the tow vehicle is in reverse....How do I add a switch on the RV that powers up the RV under-trailer lights independent of the tow vehicle? I'll use those lights for night time walk arounds etc.

[Bobbo]

momentum rv wrote:
You just need a 12v on-off-on (single pole double throw) switch. Truck rev power to one side, trailer power to other side, lights to common. The two source power will never cross and easy to wire.

momentum rv is a genius. That would work just fine. Just be sure it is a break before make switch.

[Chris_Bryant]

^^^ what he said ^^^

I don't know why everyone wants to use a relay- a single pole double throw switch, one pole from pigtail reverse line, other pole from trailer battery (fused, of course), center pole out to lights. Very simple, very easy.
Mount the switch near the pigtail junction box so you don't need to cut any wires.

[momentum_rv]

You just need a 12v on-off-on (single pole double throw) switch. Truck rev power to one side, trailer power to other side, lights to common. The two source power will never cross and easy to wire.

[goducks10]

I added backup lights to my 5er several years ago. I didn't want them tied into the reverse lights because when you put the truck in D they go out and when moving forward you can't see how far to go before starting to back up.
I wired mine directly to the battery's using a switch and inline fuse in a compartment door on the passenger side. My wife gets out anyways to check clearances so she's the one that flips the reverse lights on. Plus I can switch them on anytime which helps when setting up camp in the dark. They only shine out about 10' past and about 5' out to the sides so they aren't lighting up the whole campground behind me.

[Bobbo]

Get a 12v automotive relay and hook pins 85 and 86 to the reverse wire from the tow vehicle and ground. It doesn't matter which pin goes to which wire.

Hook pins 30 and 87 to the battery and the light. It doesn't matter which pin goes to which wire. Do not use pin 87a.

Hook a ground wire from the light to the frame. Your backup lights will now work from the tow vehicle reverse pin, but still be powered by the TT's battery.

Now, take a 12v switch and hook its pins to the relay wires number 30 and 87. It doesn't matter which pin goes to which wire. Now, you can turn on the TT backup lights with the switch without the tow vehicle even connected.

This will allow no backfeed. The two hot wire sources are never connected.

Lakeland Bob wrote:
When I mounted backup lights on my RV (and my boat trailer and utility trailer) I simply connected their positive wire of the LED back up lights to the 7 pin (center pin) of the 7 wire trailer connector.

On the RV I went to the junction box under the trailer, located the purple wire and spliced them together. Since the 7th pin was not being used and was cut short, I had to redo all the wiring to get a longer pigtail, no big deal.

As for the relay, why? Put the switch between the house battery and the positive wire to the lights, and don't use it while connected to the TV.

Or just use a jumper wire from the #7 pin (center) to the #4 pin and remove it when done.

Now THIS ^^^^^^^^^^^ will allow backfeed.

[Lakeland_Bob]

When I mounted backup lights on my RV (and my boat trailer and utility trailer) I simply connected their positive wire of the LED back up lights to the 7 pin (center pin) of the 7 wire trailer connector.

On the RV I went to the junction box under the trailer, located the purple wire and spliced them together. Since the 7th pin was not being used and was cut short, I had to redo all the wiring to get a longer pigtail, no big deal.

As for the relay, why? Put the switch between the house battery and the positive wire to the lights, and don't use it while connected to the TV.

Or just use a jumper wire from the #7 pin (center) to the #4 pin and remove it when done.

[KD4UPL]

Your plan with a relay will work fine. To make a trailer mounted "on" switch place the switch between the 12v + input to the relay and the 12v output to the lights. The switch will bypass the relay. This will allow you to turn the lights on with the switch as if the relay wasn't even there. When the switch is off the relay will turn them on when the vehicle is in reverse as if the switch wasn't there.

[FF_PM]

The tow vehicle reverse lights will switch it on when in reverse via the relay.

On which side of the relay do I add the switch? I'm wondering about back feeding the tow vehicle system. Does the relay stop that?

[K_Charles]

If it was independent of the tow vehicle, how would it know you put it in reverse? Run the backup light wire from the 7 pin back to the lights.

[enblethen]

Connect a switch at or near the batteries to the trailer battery system.