lights and power supply problem

this is in a version 2 FH13 my headligts flash on and off while driving along and sometimes the drivers side goes out completely also the lights in the cab flicker and so does the screen on my dash what could be the problem i have tried a new lcm but that didnt do anything also its taking my battery down to 24v whilst gong along at time

a fault code that has come up today in the info display system
data link MID 146
component failure
MID 140
PSID 238
FMI 12
active

can anyone help with this

 

Right live and earth cables checked and told it must be the alternator.....
new alternator fitted
new regulator fitted and still no good,at the jump start connector at the back by the batteries I'm getting a reading of 28.2 (so all is good there) and at the positive connection at the front of the cab under the grille it is only 22-24v is there another box that the power cable runs through between the battery and the cab?