welcome to Big Mack Truck Forums.
the "lightning bolt" is the trucks electrical malfunction light. it is telling you that there is an issue with the truck somewhere
this is the procedure to get the codes:
Mack Except Mid-liner: Accessing Diagnostic Trouble Codes
V-MAC & V-MAC II
Using Electronic Malfunction Lamp
The V-MAC module can blink a two-digit blink code for each of the detectable active faults in the system. These codes are displayed by the instrument panel MIL. They allow for quick diagnosis without using a scan tool.
If there is more than one active fault there is often one root cause. As a general rule, begin with active faults that involve sensors.
To diagnose malfunctions with blink codes, proceed as follows:
Turn ignition On, then wait until MIL’s two second power-up test has finished.
There must be an active fault which keeps lamp on after power-up test.
Turn speed control switch Off, then press and hold SET/DECEL or RESUME/ACCEL switch until MIL goes out.
After approximately one second, the V-MAC module will begin blinking out its two-digit blink codes. The two digits of each code will be separated by a one second idle time (MIL out).
Each blink code digit may consist of up to eight on–off flashes. The on and off time for each flash will be 1/4 of a second.
Count the MIL on flashes to determine two digit blink code.
Only one active fault will be blinked per request. There must be a separate request for each active fault if there are multiple active faults present. To display additional faults, hold in SET/DECEL or RESUME/ACCEL switch until MIL goes out. Blinking sequence will begin again after a one second delay.
If fault blinking request is repeated while V-MAC is in process of blinking an active fault, that sequence will stop and next active fault will display.
If an active fault is cleared while V-MAC is blinking that fault, procedure will not stop.
MIL will return to normal functions after every complete blinking sequence and will remain on for active faults and off for inactive faults.
If more than one fault is present, continue blink code sequence until first active fault is displayed again to ensure all faults have been accessed.