Tapping into cargo light

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

stebs

Junior Member
Joined
Nov 10, 2012
Posts
10
Reaction score
6
Ram Year
2012
Engine
6.7 cummins HO
I needed to tap into the cargo light feed to switch some lighting i added to a work trailer, so heres what I did.

The cargo light gets its power from the cluster. It is a white wire with a tan stripe that is found in the 43 pin harness to the left of the brake pedal inside the cab, and is pin 22 i believe in that harness (its right next to an orange wire). The wire went along under the door sills on the drivers side.

I poked an 18ga wire through the grommet that the parking brake cable goes through in order to get the wire outside the cab. From there, i zip-tied it up to the harness that goes clear back to the trailer plug.

Since the cargo light gets its power from the cluster, I quick-spliced a fuse holder onto the wire under the door sill panel, and butt-spliced my 18ga wire to the fuse lead. I fused this at 2 amp since it was the smallest ATO fuse I could find in my area. At the other end of my 18ga wire, i spliced in a diode (radioshack #276-1103), and then spliced my relay connection to the other end of the diode. (note: I also taped a short piece of 10ga wire alongside my first diode connection to add some strength) I also strapped a diode across the relay coil as well to use as a suppression diode (reverse polarity)(google diodes on relays for details) to stop the back emf that occurs when relay coils de-energize). I used the diodes to protect the cluster when the coil de-energizes. I then provided ground by just bolting a ground wire through an open hole in the frame.

The truck also has an add a harness on it to add a 7 pin plug inside the bed for a gooseneck trailer. I cut the B+ wire in the add-a-harness and put my relay there, so that the relay switches the B+ on and off. I had to go by actual pins on the harness instead of wire color because the add-a-harness used different colors than the truck wiring.



Here is where I quick-spliced the fuse holder in under the doorsill. The grommet for the parking brake is near the right side of the pic. The fuse holder is hard to see here, but it is right below the red butt splice at the top left of the pic. The brown wire is my new wire that I added that goes clear to the back of the truck.

IMG_20121120_160128.jpg



Here is the relay spliced into the B+ wire on the add-a-harness. The white wire is my relay ground wire that goes to the frame.

IMG_20121120_165308.jpg

So now, I can switch the power to the B+ terminal on the 7 pin trailer plug by turning the cargo light on and off. If you wanted to add lighting inside your bed, You could tap off of that B+ wire that goes to the trailer plug, as it is hot all the time, even with the key off (it is fed by the 40 amp trailer tow fuse)
 

stretch78681

Member
Joined
Jan 4, 2016
Posts
67
Reaction score
18
Location
Texas Hill Country
Ram Year
2014
Engine
5.7 squirrel cage
Good information to have. I am planning to put a set of LED running lights under the rear bumper. I wanted them to be independent of the backup lights. Since my cargo lights are now LED, I won't be running a relay; only an additional fuse at the white/tan tap.
 

w6pea

U.S.Marine Corps Veteran
Military
Joined
Dec 22, 2014
Posts
765
Reaction score
2,470
Location
San Diego, Mexifornia
Ram Year
2016 Ram 2500 "Laramie" 4x2 CC/LB SRW 6.7L CTD Leer 122 Campershell
Engine
6.7L IL6 Cummins Turbo Diesel
Good information to have. I am planning to put a set of LED running lights under the rear bumper. I wanted them to be independent of the backup lights. Since my cargo lights are now LED, I won't be running a relay; only an additional fuse at the white/tan tap.

Just about what I am going to be doing also. Thanks for the info.:)
 

kegger

Member
Joined
Feb 16, 2016
Posts
91
Reaction score
27
Ram Year
2016
Engine
3.6 pentastar
Is this the cargo light switch you guys are talking about? The little button on the left? That's the button I would like to turn on and off the backup lights with, as well as when I put the truck into reverse. Sorry about the pic some reason it fell over lol

20160625_172221.jpg
 
Last edited:

Rzrman328

Senior Member
Joined
Aug 25, 2014
Posts
5,808
Reaction score
3,143
Location
The treeline
Ram Year
2012
Engine
Hemi 5.7
Is this the cargo light switch you guys are talking about? The little button on the left? That's the button I would like to turn on and off the backup lights with, as well as when I put the truck into reverse. Sorry about the pic some reason it fell over lol

Yes.
 

kegger

Member
Joined
Feb 16, 2016
Posts
91
Reaction score
27
Ram Year
2016
Engine
3.6 pentastar
Thank you sir!
 

sbarron

Senior Member
Joined
Feb 28, 2015
Posts
3,362
Reaction score
2,276
Location
Wasilla, Alaska
Ram Year
2013
Engine
5.7 HEMI
I did the same sort of thing bit a little more complicated. I ran my bed lights, puddle (rock) lights, and aux reverse lights to two different relays isolated by a diode. I can turn my flush mount aux lights either by putting truck into reverse, turning on the cargo light with the switch or hitting unlock on the fob. The puddle lights and bed lights also come on with the fib/cargo light switch. As the two relays are isolated by the diode, only the aux reverse lights come on when the truck is put in reverse.

http://www.ramforum.com/f41/bed_lig..._mount_reverse_light_install_pic_heavy-66687/
 

shadowhawk

Senior Member
Joined
Oct 30, 2017
Posts
3,620
Reaction score
2,808
Location
Southeast WI
Ram Year
Black metallic 2016 Sport- born 05/2016
Engine
hemi 5.7 with I2 tune
resurrecting since I want to tie into my existing factory bed light and add a few LED pods or strips deeper along the bed rails. Is this a simple thing?
 

kad

Senior Member
Supporting Member
Joined
Jul 10, 2017
Posts
2,781
Reaction score
2,291
Location
Hudson Valley, NY
Ram Year
2014
Engine
5.7L HEMI
resurrecting since I want to tie into my existing factory bed light and add a few LED pods or strips deeper along the bed rails. Is this a simple thing?

I think that what you'll need to watch for is the current draw (amperage). I'm not sure what circuit the factory bed lights are on or if they are monitored by the can-bus system. If they are, then the truck may shut the circuit down if it senses more amperage draw than it expects on that circuit. To be safe, what I would do is tap the existing bed light line to trigger a relay for the additional lights and get the actual power for the additional ones from elsewhere. The +12v line for the trailer connector is a popular option for that. My truck is a '14 and does not have the factory bed lights. I'm planning on attempting to install some aftermarket bed lights this weekend and I plan to trigger a relay from the cargo light and tap as described for power. The bed lights I have draw about .7 amp total and from what I've read, 0.25 amps is the most you can overdraw the CL circuit before the truck shuts it down.

-K
 

shadowhawk

Senior Member
Joined
Oct 30, 2017
Posts
3,620
Reaction score
2,808
Location
Southeast WI
Ram Year
Black metallic 2016 Sport- born 05/2016
Engine
hemi 5.7 with I2 tune
I may just end up running new wires. I bought an in-line fuse and on/off switch. I just have to figure out where to draw power, and where to drill for the switch.
 

shadowhawk

Senior Member
Joined
Oct 30, 2017
Posts
3,620
Reaction score
2,808
Location
Southeast WI
Ram Year
Black metallic 2016 Sport- born 05/2016
Engine
hemi 5.7 with I2 tune
Kad, are you going to put a fuse in there somewhere?
 

kad

Senior Member
Supporting Member
Joined
Jul 10, 2017
Posts
2,781
Reaction score
2,291
Location
Hudson Valley, NY
Ram Year
2014
Engine
5.7L HEMI
Kad, are you going to put a fuse in there somewhere?

Yes, it's always a good idea to do so and since the cargo light feed comes from the EVIC it's especially important for this, I'd rather not have a problem with a $20 bed light take out a $500 EVIC. :) The relay draws almost nothing in normal operation (<100 milliamps for the one I'm using) so a 1 amp or even a half amp if I can find one will work fine. I might even go old school and use a glass fuse since I can get those in 1/4 amp. A 1 amp on the power line as well will keep any issues from affecting the trailer feed. I spent the weekend doing yard work so the bed lights got delayed, again.

-K
 
Joined
Oct 26, 2017
Posts
36
Reaction score
7
Ram Year
2017
Engine
6.4 L
Did you ever get this done? If so can you post a photo of how/where you spliced into the trailer harness +12v?


I think that what you'll need to watch for is the current draw (amperage). I'm not sure what circuit the factory bed lights are on or if they are monitored by the can-bus system. If they are, then the truck may shut the circuit down if it senses more amperage draw than it expects on that circuit. To be safe, what I would do is tap the existing bed light line to trigger a relay for the additional lights and get the actual power for the additional ones from elsewhere. The +12v line for the trailer connector is a popular option for that. My truck is a '14 and does not have the factory bed lights. I'm planning on attempting to install some aftermarket bed lights this weekend and I plan to trigger a relay from the cargo light and tap as described for power. The bed lights I have draw about .7 amp total and from what I've read, 0.25 amps is the most you can overdraw the CL circuit before the truck shuts it down.

-K
 

kad

Senior Member
Supporting Member
Joined
Jul 10, 2017
Posts
2,781
Reaction score
2,291
Location
Hudson Valley, NY
Ram Year
2014
Engine
5.7L HEMI
Did you ever get this done? If so can you post a photo of how/where you spliced into the trailer harness +12v?

I haven't got it done yet and given the weather, unless we get a December heat wave (which we get about 1 year in 3) I probably won't get it done until spring but I've got the parts sitting here. I'm using one of these:

https://www.amazon.com/gp/product/B0009FJ38Q

That way I'm not cutting into the existing wires and I'll have the needed feeds to put in a tailgate light bar as well.

-K
 
Top