The switch, whether for back-up cubes or front lights, will activate the relay which if using one will be sending power to both sets of lights.
You're going to have to run wire from the cubes in the back to the switch...adding a $5.00 relay would be the best and correct way to run them off their own feed from the battery.

Amperage wise in theory you could have two sets of lights on one relay if its rated high enough for it like a 50-60 amp. relay.
But again, the switch will turn on the single relay which will feed power to all lights connected to it at the same time.
Maybe someone smarter than me can correct me but all my lights have independent relays.

 

I just bought a set of 36 watt LEDs. That's two 36 watt units = 72 watts total.




I agree they should be on a separate circuit and relay.
I want them switched to activate with REVERSE gear(when the switch is on), or not when the switch is off.
I also want them to function when the car is in PARK with the engine off. Hmm.


What size fuse?
What gauge wire?
How is this done best?


First I calculated my AMPS:
amps = Watts/Volts
amps = 72W/12V = 6 amps total for my circuit. That's a 10 AMP fuse.


What size wire? According to the chart, a 10amp circuit with 3% voltage drop over 10 feet is 14awg wire. I figure the circuit is really about 20 feet, but the chart assumes a two way circuit(back to the battery for ground). Mine will be grounded at the rear of the truck.


battery > 10A fuse > switch(OFF, ON1, ON2) > Hot1 & Hot2 out.
(continued)
Hot1 > relay > fixtures > ground.
Hot2 > fixtures > ground>

OFF is totally shut down. No function.
ON1 will work in REVERSE gear. The relay will be tapped into the trailer circuit for position ON1.
ON2 will work any time at all. The only thing I can see wrong with this is, I'll be backfeeding the relay when in position ON2. I don't think it matters.



Now, got to choose a switch and relay.
TomJV

 

In regards to the back feed you can use a directional diode. I think there are links somewhere in this site that have a diagram but I cannot find them at the moment.
Just put a diode, 1n4004 from Radio Shack, between the trailer reverse wire and the relay. This blocks any current coming from the relay to the reverse wire you tapped when you operate the switch in the #2 anytime position.

I did this for my reverse lights and also for my high beam Rigid LED light bar tap.
I have a 30" Rigid light bar in my grill with a switch in the cab for always on option.
I also tapped into the bright headlight wire as a second "signal" to activate the relay so I would not fumble with the switch on back roads and just hit my brights like normal but get the LED bar too.
I also put a 1n4004 diode between the brights headlight wire and the relay so there would be no back feed to the headlight wire when I have the cab switch on.
So basically the relay has two "signal wires" to activate and send current to the lights. 1 is whatever trigger wire and 2 is manual switch in the cab. Both turn on relay.

From what I understand, diodes are directional and have to be mounted inline one way, so current only flows one way. The diodes are marked with a line on the end indicating which direction the current flows. Any current coming the other way, from the relay and switch, gets blocked so headlight wire, or in your case, reverse light trigger wire, never see any voltage.

Make sense? Sorry. I'm not electrical engineer so I can't be more technical or specific but its how mine has been wired for 3+ years without a single issue.
Danny

 

This may help.
Also if you have a trigger wire from your reverse light I do not think you can have "completely off" position on the switch in the cab.
If the trigger is direct to the relay its going to activate the reverse LED's regardless of what position your switch is in.
Unless you put the trigger wire before the switch unlike the drawing above, mine is wired before the switch so when in reverse its on..period
I personally didn't see a need for completely off. I need light 100% of the time when backing up either auto when in reverse or by switch when parked.

 

Thanks for the tips and advice guys!

 

In my scheme, I have two switched powers supplies from up front, one will supply the relay and the other will supply the lights directly. When they are off, the relay can close all it wants, the lights will have no juice.


No that I think of it, MY PROBLEM is, IF THE CAR GOES INTO REVERSE WHILST THE HOT2 IS ACTIVATED. In this case, I'll be feeding from two sources as well as backfeeding the OEM circuit. This would be bad. I definitely need a diode.


Another way I could do it, is to use two relays, one from the reverse lights and another from the bed lights. In this case, I only have a ON/OFF switch in the cab and only have to run one wire for power supply. Of course, they'll be a problem if I shift into reverse with the bed lights on. Do they make a two source relay?
Also, I don't know about tapping into the bedlight circuit. Have to scope that out. Those LED wires are TINY.


TomJV

 

http://www.the12volt.com/installbay/...asp?tid=133209


https://www.tacomaworld.com/threads/...lights.266006/




also:
These terms have given rise to abbreviations for the types of switch which are used in the electronics industry such as "single-pole, single-throw" (SPST) (the simplest type, "on or off") or "single-pole, double-throw" (SPDT), connecting either of two terminals to the common terminal.

 

You could run one 10-12 AWG wire from power supply to the back of the truck. That size would carry enough amperage for a couple of relays to be powered off of as long as your combined amperage needs do not exceed the power cable AWG.
Why do you want to tap into the existing bed lights? are you adding more LED's and you want them to trigger off the existing lights? The relay just needs a very small current trigger so your existing LED wires whilst small would be fine to trigger the relay which would then pull the actual power from the power supply wire you ran from the battery for both reverse and extra bed lights

 

What your saying is exactly what I have in mind. I'm considering using the bedlights via a relay to run the reverse fogs AND the reverse lights as well.


This is what's on my mind. In the cab, I'd like a switch to choose between these two functions and TOTALLY off.
Problem - how and where to put the switch? It's not going to match anything. I don't want to see wires. I SAS AINT gonna drill my brandy new F150 dash!
I figure I can hide a ON/OFF toggle under the dash for the few times I might turn them off completely. Then I'll wire the relay like you said with diodes to run off BOTH the bed lights and the reverse lights.
I like this because:
Manual Operation- I can turn the lights on from the bed switch or the cab(via the bed light switch)
Auto Operation - running off the reverse lights.
Totally off - for flat-land use.
TomJV

 

Did adding the cubes give you trouble with the back up sensors?