SJB Smart Junction Box
Before you even start playing with your wiring, you need to know what an SJB is. SJB stands for smart junction box. This is the little box of tricks that controls all the lighting on your Mustang. I won’t tell you where it is because you don’t need to touch it.
The SJB is a sensitive piece of equipment with low tolerances for overload. A new one is a few hundred quid so you don’t want to blow yours. This is the item that the specialists pay most attention to when doing a light conversion. The name of the game is fooling it to make it think it is doing exactly the same job, and powering the same bulbs as before.
No significantly greater loads on any existing circuits is your aim. This is why you do not just link your back lights off your front ones, or a few months later you need a new SJB. This is what the relays you will be using are for, the existing circuits will switch the relays and the actual power will come from elsewhere thus bypassing the SJB.
Switching relays and powering LED repeater lamps is about the only load you will be drawing from the wiring that comes from the SJB. These loads are minimal enough that it won’t notice.
If you see a car with it’s indicators stuck on or exhibiting some other odd behaviour with the lights, then chances are that the SJB is knackered and a cowboy did the light conversion.
