Looking to add a reverse light onto an enclosed trailer. Would like to have it light up with the reverse lights, with a switch from the man door, or a switch from the ramp door. Am I correct in thinking the best way would be just to wire each one as a power source to the light, but then add inline diodes? If so what diode is appropriate?
Trailer Wiring with Diode?
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Trailer will have it's own small battery. Not big enough to power light for any long duration of time but should be enough to load/unload.
Just trying to isolate any feeding back into the system. Essentially I want the equivalent of three independent lights on the back of the trailer.
Just trying to isolate any feeding back into the system. Essentially I want the equivalent of three independent lights on the back of the trailer.
There are are many ways to skin a cat. Here's two. They both have advantages, personally I'd use the one with the relay, because it separates your circuits like you want, and automatically selects truck power if available, saving the trailer battery for when truck isn't connected. The non relay version is far less idiot-proof since you need to check which way to flip the switch depending on if you want trailer or truck power. Also, if one switch is on truck and the other is on trailer, then you will combine the two circuits, which you don't want, and could cause high amps as the two batteries try to equalize. The only (small) advantage of the non-relay version is it doesn't need a relay.
You could also use the relay version with two SPDT on/on switches to make a house style "three way" setup so you could turn the lights on at one door and off at the other door. I'll whip up this version next.
I've excluded the proper fuses for simplicity.
![Text Line Font Diagram Design]()
![Text Line Font Diagram Design]()
You could also use the relay version with two SPDT on/on switches to make a house style "three way" setup so you could turn the lights on at one door and off at the other door. I'll whip up this version next.
I've excluded the proper fuses for simplicity.
Yes, thé trucks reverse lights Will come on when The trailer lights are Turned on by The door switches. If thats a problem, thats where you could use your diode.
Note that you cannot backfeed to The truck from The trailer batterie
If I am not concerned about battery drain on the trailer couldn't I connect trailer battery to 87A, reverse to 87 and 85. Wire them in a fashion so that when reverse is on the relay is energized and the light is powered by the reverse wire. Then when the relay un energized the light is powered by the battery alone? Then the circuits are entirely separate? Sorry for the description instead of a picture. Oh and obviously add the switches before the light. Thanks for the help!
.Yes, drawing it is SO much easier to critique, so...
The way you describe, you would ONLY have trailer backup lights if one of the door switches was ON, and since your trailer has a battery, the lights would be ON all the time.
Why do you want to do it this way?
If it's to eliminate the truck reverse lights coming on when you turn on a door switch, then you should just add a diode.
Like this:
![Text Line Font Diagram Circuit component]()
I've never used a diode for that purpose but I *think* that's how it would work.
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what the hell are you designing?most oem trailer plugs are similar to this pic and have the backup lights included in the wiring
same goes for the aux 12v+ charging for the trailer battery, this is also good for connecting interior/exterior lights
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if you have a standard 7 pin plug on the trailer there is no back feed it is the same 12 volts
installing a $40 diode doesn't make sense at all
just install spdt on-on switch in the back up light circuit
two 12 inputs: reverse light circuit and 12v constant
one output: to the lights
I am thinking this set up, but move the spdt switches to before the relay.
Relay energized by truck reverse light - truck reverse light powers trailer lights
Relay un energized, trailer lights can be switched on be either spdt switch.
I would like to be able to turn on the reverse/exterior lights on the trailer while plugged into the truck, and not have the reverse lights come on in the truck if it isn't running. The power in this situation would come from the trailer battery. Maybe it wouldn't back feed into the truck lights on the newer trucks but it seems like 20 minutes of wiring and a cheap relay totally isolates the systems.
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for the trailer battery to charge it needs to be connected to the truck
anytime you discharge the trailer battery while connected to the truck you also discharge the truck battery
if you install a diode the trailer battery will never charge
thousands upon thousands of trailers wire lights into switches
the only thing different you want is to be able to switch the reverse lights on independent of the truck
install a spdt switch will accomplish what you want, no diodes or relays required
lights on in one position, reverse lights in the other position; simple as that
i recommend these lights off of ebay: small, bright as all hell and low draw
i run these as headlights on my golf cart
4 of them for $34 on ebay 18W-FLOOD-CREE-LED-LIGHT-BAR-WORK-LAMP-FOG-12V
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Yes, that's essentially what I'm using the relay for in my post above yours.for the trailer battery to charge it needs to be connected to the truck
anytime you discharge the trailer battery while connected to the truck you also discharge the truck battery
if you install a diode the trailer battery will never charge
thousands upon thousands of trailers wire lights into switches
the only thing different you want is to be able to switch the reverse lights on independent of the truck
install a spdt switch will accomplish what you want, no diodes or relays required
lights on in one position, reverse lights in the other position; simple as that
i recommend these lights off of ebay: small, bright as all hell and low draw
i run these as headlights on my golf cart
4 of them for $34 on ebay 18W-FLOOD-CREE-LED-LIGHT-BAR-WORK-LAMP-FOG-12V
![]()
But this will work. Del City - Item #: 7200033
Lights to the middle, reverse to one outside, trailer battery to the other outside.
Well, I actually listened to what the OP wanted, and designed a circuit that was as simple as I could make it, while still providing what the OP wanted.
The "backfeed" isn't about the trailer battery charging the truck or whatever, it's simply about the truck reverse lights not coming on powered by the trailer battery, which makes sense as it will reduce the load on the trailer battery.
Wiring it like this you would ONLY ever be able to turn on the trailer reverse lights when the truck is connected.
Can you draw what you're talking about here, and also explain what this change is meant to accomplish. I don't think this circuit will operate how you want.
This is the part that makes the diagram slightly more complicated, no big deal.
Will do.
That would work fine, except for the truck lights coming on from the trailer battery when the light switch is turned on, which OP doesn't want.
The trailer battery will still charge through the trucks "aux 12v/chargin" pin. We're not changing that circuit at all. The only thing the diode will do is prevent the trucks reverse lights from coming on from the trailers battery.for the trailer battery to charge it needs to be connected to the truck
anytime you discharge the trailer battery while connected to the truck you also discharge the truck battery
if you install a diode the trailer battery will never charge
thousands upon thousands of trailers wire lights into switches
the only thing different you want is to be able to switch the reverse lights on independent of the truck
install a spdt switch will accomplish what you want, no diodes or relays required
lights on in one position, reverse lights in the other position; simple as that
i recommend these lights off of ebay: small, bright as all hell and low draw
i run these as headlights on my golf cart
4 of them for $34 on ebay 18W-FLOOD-CREE-LED-LIGHT-BAR-WORK-LAMP-FOG-12V
![]()
Just because "thousands of trailers" are wired one way, doesn't mean it's the right way. 99% of people who buy trailers don't give a damn how what's wired, nor could they even comprehend the differences if you tried to explain them.
-ogre, I know you're no dummy and you can read a print, so I don't understand why you're arguing against a requirement the OP wants.
I'm confused.
Why don't you draw up a sensible, simple as possible diagram with no relays or diodes that fullfills the OP's requirements:
*trailer reverse lights ALWAYS come on when truck is in reverse.
*trailer reverse lights are powered by truck when truck is plugged in and running.
*trailer reverse lights are powered by trailer battery when truck is not connected or running.
*truck reverse lights come on when truck is in reverse
*truck reverse lights are NEVER powered by trailer battery
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