Let me look for information on your Mustang.
The first thing you need to do which is the first step in the diagnostics is to check the fuse. It is fuse #67 30 amp fuse. Let me know how the fuse is and I will continue researching.
There is also fuse 59 and fuse 63 both of them are also 30 amp fuses. These all power up the headlight circuits and module.
Did you check the bulbs to make sure they are ok? If they are ok do you have any way of checking for codes in the body controller? I can try to send you the diagnostic information
One of the other easy checks to do is to swap the high beam relay with another relay of the same part number. The relay is located in the fuse box under the hood.
Goes with B4
That is all of them.
what is sjb self-test,c1050,DTC B2598,SJB C2280C,circuit 1708,BEC C1035A,PID,wiring diagrams cell 149,
SJB (Smart Junction Box) is a fuse box with a built in module that you can retrieve codes from.
C1050 is a connector
B2598 is a code that would be stored in the SJB for headlight relay circuit failure.
C2280c is one of the connectors on the SJB
Circuit 1708 is one of the wires in the system
C1035A is a coneector in the engine compartment.
PID is a parameter index. This is the reading that you are looking at on the scan tool when you are watching live data.
Cell 149 wiring diagram is one of the diagrams of the electrical circuit let me see if I can pinpoint which one.
Cell 149 is a diagram of different components that show which circuits need tested.