be careful. I’ve tried this and threw a DTC on the BCM, killing my bed lights and upper brake light if I remember correctly. The wire to the bed lights is the thinnest electrical circuit conduit I’ve seen not on a circuit board ! if you add anything to it, that will probably push it to the limit.
I can tell you that 3 amps rated draw is too much, I am not able to say how much you can add without trouble.
good luck !
This is exactly right. The majority of lighting outputs from the BCM are controlled by Field Effect Transistors (FETs). They monitor circuit current, and will set DTCs if the current draw is out of range.
There are multiple thresholds that must be met before the BCM will disable the circuit output. Therefore, you could have a DTC set and there would not be any visual indication of it. Once that DTC continues to be present over a predetermined amount of cycles/time, the BCM will permanently disable the circuit and the BCM will set an internal failure DTC, which requires replacement of the module itself.
The system is not designed for any load in excess of the factory component draw. That includes relays as well. The only time relays can be used is when the relay is replacing the original component, such as when an upfitter removes the factory incandescent lamps on a chassis cab and uses a relay to power LED lamps. The relay substitutes for the load drawn by the factory incandescents. If the LEDs were replaced without using the relay, a DTC would set for the current draw being too low (open circuit).
