Intermittent electric failure all warning lights keep flashing on/off

Hi, my vehicle has an intermittent electrical problem where once the engine starts all the warning lights, 4WD, ABS, oil and check transmission come on and the truck slips into safe mode (third gear) and even sometimes stalls. The problem is very erratic, sounds like a solenoid clicking and if I switch it off and leave it, whatever it is also drains the battery after ignition key is removed.

This started a couple of years ago with only the check transmission light and ABS light coming on but it would soon go out again and the truck would be okay. It has deteriorated over time and now I cannot drive the truck as this issue keeps draining my battery and if I do start it and run it slips in and out of safe mode.

Can anyone advise what electronic part might have failed? Is it a sensor or the entire computer that is failing. I do not know what to check? Please advise. Thanks.