I'm wanting to install LED flood lights on the bumper of my 5th wheel for reversing but only want the lights to come on with the use of an upfitter switch. I want to utilize the center pin of my 7-pin connector in the truck bed, which is for reverse lights. However, I don't want the power to this pin to be controlled when the truck is put in reverse. Instead I want to just turn the power to this pin on/off with an upfitter.

Does anyone know where to locate the wiring for the bed connector up in the engine compartment?

I'm hoping if I can identify the reverse wire, I can just snip that, cap off one end (to reconnect later if I need to), and then wire in the other end to the upfitter fuse box.

 

Just a thought- It may be easier to simply introduce a 12v relay at the 7-pin connector itself that you controlled via the upfitter switch. If your trying to use the "Reverse" lights without shifting into reverse then a separate 12v wire from the upfitter switch to the 7-pin connector would be needed.

you might include your truck info to get info on a wiring or connector location

 

Thanks smikesF350 for the reply!

I have a 2017 F350 Lariat, crew cab 6.7L powerstroke.

Since posting and spending a bit of time under the hood trying to figure out the wiring, I came to the same basic conclusion - run a new wire from the upfitter fuse box to the 7-pin connector in the bed. Just snip the wire, cap the existing wire and connect to a new 12v wire connected to an upfitter relay under the hood. In fact, I think I'm going to run a whole wire loom with a couple of spare wires for later use (on-board air compressor, etc.).

I'm not too familiar with relays. Since the reverse light wire only goes hot when the truck is put in reverse, how would a relay, controlled by the upfitter switch, be able to power the reverse light wire without the truck being in reverse? I figured I'd just have to run, say, an 8 AWG hot wire all the way back to provide direct juice to the reverse light pin.

Appreciate the help.

 

SuperJep,

A relay would allow more power to the lights you are installing in case they need more amperage than the skinny oem reverse light wire allows to flow through.

It does not sound like you ever will want trailer lights to go on automatically so your simple plan should work. However, if you ever power a device (or light) from two or more sources, with or without a relay, you should install


This prevents current back flow to the other source.

 

I did a quick search. This is a basic wire diagram. The relay is avail at most auto parts stores and you might even find a socket with pigtails. #86 and #85 pins energize the relay. #30 carries the current to pin #87 or your lights. The idea as pointed out in the previous post, not to have high current draw running thru a light duty switch. The link is below. If your upfitter switch is powered, then swap out the pin #85 to +12v from the upfitter switch and make pin #86 ground. If you go with LED Back Up lights, 8AWG might be overkill. Then again, having a high current wire terminate at the rear of your truck is not a bad thing for future projects. Fuse the wire at the battery end!! This is an after thought- The diode referred to in the previous post could be used to allow both a manual and automatic (shifter) operation of the reverse light.


https://www.easycarelectrics.com/aut...agram/Terminal

86 wire of the relay’s coil circuit is connected to a hot power source, while terminal 85 is connected to a light switch, which is often a ground power source.

A fused wire comes from the fuse box to terminal 30 of the high amperage circuit, while the second terminal 87 is connected to the headlight. The coil circuit consumes almost 0.5 amp current, which is a not burden on the light switch, as a result, will not burn the light switch.

So, when the coil circuit is activated, the high amperage circuit will make the contact, and the current will directly flow from the fuse box’s battery connection to the lights and the light will illuminate.

 

Wow, thanks for such great information and help!

So I drew out what I'm understanding from your previous 2 posts with what I have in mind. I'm planning to put 2 pretty nice bright LED floods on my 5th wheel trailer bumper to light the area behind ( ) down the sides of the trailer (3 each side) to illuminate the area around me when I'm backing up. I don't plan to ever turn these lights on automatically when shifting into reverse (might freak out drivers behind me!). The total wattage for all 8 lights looks to be 152W = 12.67Amps. So given about 20' of wire length from the battery to the back of the truck, I calculated 8AWG wire. But in the future I'd like to install an on-board air compressor, so maybe a 6 or 4 AWG hot wire might be better?

So basic approach at this point would be:

• Run new hot wire directly from the battery (fused near battery) to the back of the truck. Bundle this in a wire loom with maybe 3 smaller relay wires to be connected to upfitter switches (2 for future use).
• Connect new hot wire to pin 30 of reverse lights relay at back of truck.
• Connect Upfitter switch, via the upfitter relay/fuse box under the hood, to one of the smaller relay wires that run to the back of the truck and connect to reverse lights relay pin 85.
• At 7-pin connector, snip reverse lights pin wire, cap off existing wire, wire up pin 87 of the relay to the reverse lights pin in the 7-pin connector. Ground relay pin 86 to truck frame.
• Add in diode to prevent current back flow to other future devices drawing off the shared hot wire (not sure where diode would go in line - before or after relay?).

Hope that all makes sense.

 

I had to re-draw your drawing to get a better feel for the flow of current. I think I got a good understanding of what your doing. I attached it below.
Base on what your doing and that you are NOT trying to power one accessory from two different sources of 12v, you do not need a diode. Think of a diode as a diverter water valve. You have two sources of water- one from a well and the other from your utility supplier. using the valve ie-diode, you have the ability of choosing which source you are going to use to fill a pool. It's either one or the other, but not both. The diode in a DC application prevents current flowing back to either of the sources of 12v. Effectively isolating the two switches from each other.

The way I see it, you have three different accessories planned- Compressor, side lighting (both sides) and the back-up lighting. So unless your planning on lighting up the world around you all at the same time, you need to use three upfitter switches and three relays. If you want to have the option of picking the left or right side lights independently then you need a 4th switch and relay.

I think you better off with a #6AWG mostly because of the current draw of a compressor. I commend you for doing the math. I pretty much go by my gut guessing and don't get to caught up on large current draws when using LED lights. But your planning on 8 of them and that could be a fair draw. If your gonna use the existing wire on your trailer from the center pin 7, then it would be a good idea to find it on the trailer side to see what size the OEM used. It might be insufficient to power all 8 lights. Ya might consider add fuses between the relays and the lights.

 

SuperJEP,

I agree with sMikesF350 and his water analogy. You do not need any diodes in your plan. A diode is only recommended to be used if you are setting up so that your reverse lights always go on when in reverse and you want to add the option of also manually turning them on in park or any gear.

I do not think it is needed, but if for some reason you wanted to turn on the compressor from the cab via upfitter switch and also have a switch in the bed to turn it on, you would want to use a diode. Inputs for diode come from both switches. Output from diode is to the compressor (but a much better diode output usage would be to activate the relay that allows full amperage to flow from your 4/6 gauge wire to the compressor). Note, you can buy relays that activate by providing ground to the activation connector, others can be bought that activate when power is supplied to the activation connector. Make sure you get the correct relay, and if using power to activate the relay, that source should also be fused preferably before your switch. That fuse would be light blow, whereas the 4/6 wire would have a high amp fuse or circuit breaker at the end closest to the battery.

 

Not sure why you don't just run a wire from the Upfitter to the lights you want to switch?

Under my rear bumper I have 2 lights connected to the Reverse and 2 more lights on an Upfitter.

 

Thanks smikesF350 for the re-drawn diagram! Awesome. That's pretty much exactly what I want to do. Except that I planned to have ALL the lights come on with the one upfitter switch. Firstly, because I don't plan to use these lights for regular reversing - after all, many trailers don't have reverse lights. I plan to use them when I need to back my 5th wheel in the dark. So the side lights are also needed to illuminate around me, especially where the wheels are going. So I basically do want to light up the world around me!! Secondly, I only have one available pin in my 7-pin connecter in my truck bed. So unless I were to install a new hookup and separate wire to my trailer, I wouldn't be able to have two separate circuits to my trailer that I could control directly from 2 separate upfitter switches.

MagicMtnDan - My combined draw from all 8 lights would be 152W = 12.67Amps, so calculated that the size of wire running from the upfitter relay/fuse box to the 7-pin connector in the bed, wasn't going to be big enough. Plus, it'd mean finding that wire up front under the hood and tapping into it before it's controlled by shifting into reverse. Gave up on that pretty quickly! Maybe it works for your setup because the draw isn't as high and maybe since reverse lights aren't typically on for that long, so as long as it doesn't blow the fuse, maybe the wires wouldn't have enough time to really heat up. Plus, I want to eventually add in an on-board air compressor, so figured I'd bypass all the headache of worrying about wire sizing and monkeying with the factory wiring, if I just run a new positive directly from the battery and then I've got a nice power supply at the back to tap into for future use.

DrMatt - Wondering what power distribution block you used mid way under your truck to tap into? Could you post a link?

Once I get this project underway, I'll post some pictures and notes.