I need help fast, i was going out to the truck and tried to use the key fob and it didn't work, so thought oh well battary in fob is dead so i unlocked the door with the key and the alarm went off for 1 second and then went off. Then the key fob worked. But when i started going down the road the stereo was cutting on and off, i was getting the airbag light, the lights would dim back and forth, the check gauges light would come on. It thru 2 codes that say unknown on the smarty. PD403, and PD421. I took the truck back to stock also. and did the same thing. Any suggestions

 

If it were mine, I'd check the battery cables and any grounds I could locate. When I worked at Landrover they put some of the grounds on over paint and it was only a matter of time before weird problems like yours started to show up.