I recently installed some LED light strips in the bed of my truck and tied them into the factory bed lights. I hooked them up and tried each strip as I was wiring them and they worked fine. Finished up and I pushed the factory lights back in place and tried to turn them on again, they came on for a second then turned off. Started the truck, turned it off, pushed the bed light button and they worked. Drove home and tried the lights again, worked fine. Went back out later to put something in the truck, pushed the switch and the lights came on for a second then turned off. Tried again this morning and they work as they should. Light on the back of the cab works as it should. When the bed lights stop working neither switch, in the cab or in the bed will work.

Having read through a few threads I am thinking it is probably the switch in the bed so I have ordered a new one.

Seems like the most common symptom of switch failure is the lights coming on by themselves. Is it also the case that when the switch is faulty that it would not function as it should, by turning the lights on?

I ordered the switch that has been referenced in several other threads, Motorcraft SW-7733. When searching I also found another switch that looks exactly the same but it is indicated to be for the Superduty trucks, Motorcraft FL3Z-9C888-B. My curiosity got the best of me so I searched for aftermarket switches and found some available that are described to work on all of the different truck models. Anyone familiar with the 2 switches and know if they are interchangeable?

Crazy that a cheap plastic switch has been the cause for so much frustration for so many people.

 

FL3Z-9C888-B is the Ford part number for Motorcraft SW-7733. They are the same part. The switch inside the plastic housing is a momentary mircoswitch. The BCM monitors the switch circuit for a momentary connection to ground (which is made when you press the switch). The BCM then turns the bed lamps on. Pressing the switch again turns the light off. If you leave the bed lamps on, the BCM has a timer and shuts them off after a period of time.

Your problem may not be the switch. The bed lamps are controlled and powered by the BCM White Light FET (Field Effect Transistor) circuit. The FET monitors circuit current draw and, if an over-current occurs, the circuit is turned off until the next Off/On ignition cycle. The FET auto-resets on the ignition cycle. If too many over-currents are detected, the BCM sets a DTC and the FET remains off until the problem is corrected and the DTC erased. Your added bed lights may be drawing just enough current to trip the FET sometimes. A scan of the BCM for DTCs would confirm if this is indeed happening.

 

Thank you for the info, you sir are a wealth of knowledge!

I have a tuner that I can read DTC's so I will connect that and see if I have any codes.

If it is the case that the strip lights are causing the circuit to overload wouldn't that cause all of the lights on the circuit to shut down? Only the strip lights are shutting off, the cargo lamp at the top of the cab is still operable.

If it is a case of overloading the circuit is there an option to switch out some bulbs elsewhere in the circuit and reduce the overall draw?

 

Be careful. Your tuner may not be able to communicate with the BCM.

The cargo lamp on the CHMSL is run buy the Puddle Lamp FET, a different circuit.

 

Got it. I was just thinking if it threw a DTC the tuner would be able to read it. How could I go about reading the BCM dtc's, forscan? I do not have that but my son does.

When I got home from work I opened the tailgate and pushed the switch, lights came on for a second and shut of, circuit tripped. I started the truck and shut it off, pushed the bed switch and the lights came on and stayed on. I did this about 10 times and it worked fine. Whatever is going on is intermittent and makes no sense to me. I would think that if the added lights are creating an overload it would be consistent and cause the fault every time.

Could the issue be a loose or broken wire, a dirty or wet connector?

I have a new switch on the way and will start with that, the one on the truck is the original, so almost 5 years old and the screws on the back are corroded really bad. If the switch does not correct the issue I plan to remove the factory bed lights and see if the strip lights will function properly. If that fixes it then I would assume it is an overload to the circuit and I will just leave the factory lights out. I can't say that I was impressed at all with the factory lights, they do not put out a lot of light and when I put my cargo divider in it will block most of the light anyway. The LED strips are great and provide light along the length of the entire bed, had them in m previous truck and the reason I put them in this truck.

 

I have done some research on the light strips that I installed and found that each strip draws 3 amps, so both strips together are drawing 6 amps.

Is there a spec for how many amps the bed light circuit will allow before overloading?

What is the amp draw of the factory bed lights? If I remove the factory lights am I freeing up enough capacity to power the led strips?

Based on output of the lights I would prefer to have the led strips over the factory lights. If the factory bed light circuit is not sufficient to power the led strips what is my course to correct, other than wiring directly from the battery, which is what I did with my previous truck.

 

I don't know what the current level trips the FET. I assume it is different for each FET circuit within the specific module (BCM in this case).

Disconnect one side and see if the problem goes away. If you prefer the strips, then disconnecting the OE lights would be an option, if in fact, the circuit is being overloaded.

 

I disconnected on of the light strips and now the button seems to be operating normally. Preliminary results show that you were correct about the overload. When I get a few minutes I will disconnect the factory lights and reconnect the strip and see if they work without tripping the circuit.

 

Today I tried the switch again, with just one LED strip hooked up along with the factory lights and it tripped the circuit. Guess I will just have to run a fused line from the battery for the LED strips. Not that I mind doing that was just hoping I could go the easy route and tap into what was already there.

 

Have you confirmed your are tripping the FET with a DTC scan or are you just assuming that is happening from my descriptions? It could still be an issue with the switch.