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Cargo light woes

44K views 23 replies 9 participants last post by  Charger_ff 
#1 ·
I just traded in my Chevy 1500 for a 2008 F-350 crew cab longbed SRW.

I'm new here by the way...hi, I'm Ryan, and I love trucks. I'm great at fixing them, but electrical is my weak spot.

I've searched the google machine, and I've done a search of the forum, and haven't been able to solve the problem. I can not get my cargo lights to turn on. First I checked the fuse. Fuse #10, 15 amps, not blown, and getting voltage. Check. Then I put a brick down on the brake pedal. 3rd brake light turns on. Swapped bulbs with the cargo lights, and all 3 bulbs up there work. Checked voltage at the cargo light plug...nothing.

I've got the dimmer switch all the way up past the detent and the doors open. The courtesy lights in the dome turn on.

Where does the power for the cargo light actually come from? How can I get it to come on? Alldata has nothing about the cargo light except the part number for the bulb, and nothing about it in the wiring diagrams. I'm at a loss.
 
#2 ·
Actually I did just find some stuff on alldata about it. Looks like I might need a new SJB. But I also got some LED lights that mount under the bed rails and put them on an upfitter switch. I could try to get the cargo lights on the same upfitter, or just ignore the problem. For $125+ I don't want to replace the SJB.
 
#5 ·
It does seem by the wiring diagram I have is that the cargo light is turned on by a Violet (vt) wire out of the SJB (11-3) on pin 12. Might want to take a meter and measure it there if there is 12 volts on the output (Pin 12). If you don’t have it there, the input to the SBJ might be a problem.
 
#6 · (Edited)
Progress:

I started over with the alldatadiy.com troubleshooting for cargo light inoperative.

Step 1: Apply the brake pedal. Does the highmount stop light illuminate? If yes, proceed to:

Step 2: Key in off position. Disconnect SJB C2280c. Connect a fused 10A jumper wire between SJB C2280c-12 harness side and battery positive. Note: If fuse fails, repair circuit CLN25 (VT) for a short to ground. Does the cargo light illuminate?

The 10A fuse blew, so now I need to repair circuit CLN25 (VT) for a short to ground. I have no clue what this circuit is, but I'm guessing it's the wire that goes to the cargo light. So I should test connectivity between the cargo light positive connector and ground. I should have a ground if it's shorted. edit: Disconnected the highmount light from the harness. I got a confirmed ground from pin 12 on the SJB connector, and also from the highmount connector positive lead. As for repairing it...I have no idea how to find a ground without pulling out the whole wiring and looking for a bare strand, and I REALLY don't want to pull the headliner.

In the wiring diagram CLN25 (VT) is a purple wire going from the SJB to the highmount light and the running board lights. I don't have running board lights, so I think I can assume the short is between the SJB harness and cargo light.
 
#8 · (Edited)
A little FYI for you - you need to know this before you condemn the SJB or fail to diagnose this properly. The cargo light is tied into the factory running board lights (if equipped) and is on what is called the "puddle Light" circuit which works with the courtesy lamps but on a completely different circuit. This circuit, along with many on the 2008 and newer Ford trucks, is a FET circuit which means Field-Effect Transistor (FET) Protection. The Smart Junction Box monitors the circuit for low amperage, over amperage conditions and is capable of setting codes to aid in diagnostics. This protection mode also DISABLES the circuit if a high load or short circuit condition is continuously detected. The circuit protection in most cases and depending on the type of failure is not reset until the code is cleared from the module. So, if you go looking for voltage for example , you are not going to find it until you correct the source of the high load or short to ground and clear the code depending on the level of the fault. Knowing what codes you have is also important as certain codes will indicate a failure with the module thus saving you a lot of time accessing wiring and inspecting and testing.
 
#10 · (Edited)
A little FYI for you - you need to know this before you condemn the SJB or fail to diagnose this properly.
I'd like to point out that:
1) the OP used a reasonable descriptive subject line in the initial post; and,
2) Ford Doctor gave a succinct and precise reponse.
and, therefore future searchers looking for help on this subject should be able to address their problems pretty easily.

It drives me crazy to see posts here with non-descriptive non-detailed subject lines such as "please help with my problem".

Just a minor rant, and a big thank you to all the experts here who give so freely of their time and expertise!

- Don
 
#9 ·
Thanks ford doctor:
Your knowledgeable information is always appreciated by me and the forum members.

C9h13no3:
I myself wouldn’t assume that because I don’t have running board lights that the wiring wouldn’t be there for then (I was counting on it), I bought and was going to install lights for the running boards (the dealer I have thinks that every thing I do to my truck voids the warranty, so I didn’t).

Maybe ford doctor can rule it out that only the wire to the cargo light is there? The previous owner might of did some wiring that is causing your problem and I would check that before pulling down the headliner, The wire harness might not even go through the headliner from front to back? It might run along under the floor with the sub woofer wires? I don’t have my truck here or I would check it.
 
#11 ·
I have an Actron pocket scan plus that I hooked up, and it did not read any DTCs, and when I do the setup > reset to do a system check on the dash it comes up clean.

It's raining today and I can't get the truck in the garage, so I'm going to hold off on any electrical work.

Thanks for the explanation ford doc. I'm guessing it isn't sending voltage because it's shorted, and now it's my job to find the short.
 
#12 ·
I have an Actron pocket scan plus that I hooked up, and it did not read any DTCs, and when I do the setup > reset to do a system check on the dash it comes up clean.

The lighting is not a function of the dash or instrument cluster...

You need to test the SJB (Smart Junction Box) which is still also commonly referred to as the "GEM." I don't know what non-OEM scanners would list it as.
 
#15 ·
#18 ·
Thanks for the Update.
Glad you to here you got it done for free.
 
#20 ·
08 F-250 as well, and today I noticed that my bed cargo light is not coming on, replaced both light bulbs and still no light when I open the door or push the instrument dimmer switch all the way up. Third brake light is working. Any ideas I should try?
 
#21 ·
2009 F250 Super Duty Cargo Light Not Working

I purchased used a 2009 F250 Super Duty. The Cargo lights did not work and neither did the high mount brake light. The interior light worked and the instrument panel dimmer would turn on the interior light as it was supposed to do. After removing the high mount light assembly, I found the bulb sockets to be burnt with all three of the bulbs burnt out. I replaced the light housing assembly that I bought at a junk yard and I replaced the bulbs and the high mount brake light worked but the cargo lights still did not. After reviewing the wiring diagram, I found the blue wire coming from the Smart Junction Box in the passenger rocker panel. I energized the blue wire and the cargo lights came on. So, it was apparent that the issue was with the Smart Junction Box. With the information learned in the above posts, I have a friend who is a Ford engineer and he was able to check the Diagnostic Trouble Codes from the Smart Junction Box. Sure enough, a code was present in the Puddle Light circuit indicating a short to ground in the circuit. Since I had already repaired the light bulb sockets and replaced the bulbs, this had taken care of the short to ground. All we had to do was clear the DTC and the cargo lights now work. The information about the SJB automatically turning off the circuit is correct and the only way to turn it back on is using the Ford IDS tool.
 
#22 ·
Maggieillini you are correct that clearing the code for a disabled FET circuit will restore function provided the fault is repaired and it is capable of passing a self test. This is a minor detail but important to be aware of if you are a do it yourselfer. It poses a minor inconvenience if you do not posses or have access to a scan tool.
 
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