How-To: GMT900 Cargo Light Mod.

dlewis1111 · February 1, 2010

Great info here. Just finished this simple little mod. I am going to look into installing higher powered bulbs tomorrow. It would be cool if I could fit 55w driving light bulbs in there!

elcompalaline · February 2, 2010

Great info here. Just finished this simple little mod. I am going to look into installing higher powered bulbs tomorrow. It would be cool if I could fit 55w driving light bulbs in there!

Cool! They do seem a little dull don't they? Let me know what you come up with, I wouldn't mind upgrading those things.

dlewis1111 · February 2, 2010

Great info here. Just finished this simple little mod. I am going to look into installing higher powered bulbs tomorrow. It would be cool if I could fit 55w driving light bulbs in there!

Cool! They do seem a little dull don't they? Let me know what you come up with, I wouldn't mind upgrading those things.

I just order LED bulbs to fit in there from LEDLIGHT.com, and will post some pics. Also ordered interior lights and looking into reverse lights as well. These are pretty cheap IMO.

http://www.ledlight.com/SearchResult.aspx?KeyWords=34256

elcompalaline · February 3, 2010

Great info here. Just finished this simple little mod. I am going to look into installing higher powered bulbs tomorrow. It would be cool if I could fit 55w driving light bulbs in there!

Cool! They do seem a little dull don't they? Let me know what you come up with, I wouldn't mind upgrading those things.

I just order LED bulbs to fit in there from LEDLIGHT.com, and will post some pics. Also ordered interior lights and looking into reverse lights as well. These are pretty cheap IMO.

http://www.ledlight.com/SearchResult.aspx?KeyWords=34256

Can't wait for the pics!

dlewis1111 · February 7, 2010

I installed the LED lights into my cargo light and oh my gosh are they a thousand time better! I also did interior lights at the same time and they look great too. I can't understand why people like Putco sell interior light kits for 150 plus when the bulbs are actually very cheap. I will post pics when it gets dark again.....

brims · February 7, 2010

I installed the LED lights into my cargo light and oh my gosh are they a thousand time better! I also did interior lights at the same time and they look great too. I can't understand why people like Putco sell interior light kits for 150 plus when the bulbs are actually very cheap. I will post pics when it gets dark again.....

Because they can.

BigBlueLB756 · February 7, 2010

Sadder than that, it's also because there are those out there that will pay those prices and think they got better stuff than if they'd hunted up the parts, like most people on here do.

dlewis1111 · February 8, 2010

Here are the pics! I also included the interior light pics, although that one is hard to tell......First one of the interior bulbs

Hard to tell on this one how much brighter the interior is. Absolutely no heat from them either.

SOOOOOOOO much better

Didn't think of this one, but if you decide to tailgate me take this!

I looked into swapping all the bulbs, but I don't want to fool with the inline resistors needed to maintain proper resistance in the system so that the flashers will operate properly.

I am going to change out the reverse lights though. Will post again with those pics, and I may change to a three way switch that allows off/cargo light only/ cargo and reverse together

elcompalaline · February 8, 2010

Sweet, now going to check the bulbs out in the link you provided. Thanks for the pics!

dlewis1111 · February 14, 2010

Just ordered the reverse lights too, and am adding a three way switch that will allow me to control the cargo, reverse, or both all together. Will post pics.

Pumper · July 2, 2010

From what I understand it isn't necessary to put an inline resistor in place in these trucks. The GMT900s don't have flasher modules, the system is controlled by the BCM. The truck just needs to be programed at the dealer to ignore burned out bulbs. This is the way all of the Cab-Chassis trucks are programmed from the factory.

07VMax · July 21, 2010

i dont understand why the new trucks dont have a seperate button for the cargo light, my 04 had it and i used it regularly to check what was in the bed

dlewis1111 · July 23, 2010

From what I understand it isn't necessary to put an inline resistor in place in these trucks. The GMT900s don't have flasher modules, the system is controlled by the BCM. The truck just needs to be programed at the dealer to ignore burned out bulbs. This is the way all of the Cab-Chassis trucks are programmed from the factory.

You are correct when you say that there are no flashers and that they are controlled by the BCM. Having said that, have you tried to get the dealer to reprogram the module with the chasis model specs? I have and they look at me like I am nuts. I even showed the paperwork to them on how to do it and they refused. That puts me back to using resistors to emulate the proper resistance and I am not willing to do this.

bwpiper · July 29, 2010

can you engage your cargo light while driving or is this only for separating the cargo light and interior lights?

bwpiper · August 3, 2010

ccan you engage your cargo light when you are driving?

After a fellow member (brims) posted up the necessary info on the wiring for the cargo lights(here is the link, post #11), I went ahead and traced the wiring and installed a rocker switch allowing me to turn them on without the interior/domes. A feature that was so useful in my 04 but not present on NNBS GMT 900s, perfect for those of us with stuff in the bed that could be checked on from the interior of the truck. Here is my "How To".

Note: For anyone doing this mod, please be very careful and place close attention to what you are doing. You will be working near the BCM and junction box if anything would go wrong, I will not be held responsible and this mod should be done at your own risk. With a little patience anyone can tackle this just watch what you are doing.

Tools needed

-wire stripper/crimper

-flashlight

-electrical tape

-electrical tester tool

Materials needed

-(1) rocker switch ($7.49)

-butt connectors ($2.99)

-female wire connectors ($2.99)

-(1) Add-a-circuit ($9.99)

-18 gauge wire (not sure on the price, I had some around from another project)

Find your BCM (located under the steering wheel area). On the BCM, the pink connector runs the cargo lights wire (tan wire w/brown line) to the junction box (located a bit lower than the BCM and closer to the fire wall) into a brown connector. This is the wire we need to cut right before the junction box.

Once the wire is found, it was time to find a power source. I used the Add-a-circuit and plugged it into the Aux Pwr slot located in the fuse area in the trucks interior (between driver door and dash). The Add-a-circuit has two slots for your fuses, I used (2) 20A fuses to prevent a short.

Find a place to mount your switch, I used a little cubby hole under the HVAC controls between the two cigarette lighter plugs. You can mount it any where else that may be easier for you, I just like that when off it is not in plain view. But when on, I can easily see it and remember to turn it off so I don't accidentally drain the battery. Then run your wires behind the dash near the fire wall.

You will need (3) wires from the switch.

1.power (this will connect to the Add-a-circuit in the fuse area)

2.ground (I used a self tapping screw and grounded on a dash support just to the right of the gas pedal)

3.accessory (this will be connected to the tan w/ brown wire that controls the cargo lights. It is very important that when you connect this wire, the connection be made to the part of the wire running towards the junction box and not the BCM!)

Make all of your connections, try out the switch to make sure it works properly and then put everything back together.

Here is the finished product, you can clearly see that the cargo lights are on. Also my interior/domes are not on and of course the rocker switch is also on (it has a nice bright red led). I also made sure I retained the OEM features of my interior lighting by opening closing the door and using the dash switch to manually turn them on. Everything works like a charm and I now have the ability to turn on the cargo lights without the interiors when I want to. Enjoy!