I dont see why you cant tie it into another 12 volt source as long as it has 12 in start, run, and on. Not sure if you will be in the 2nd gear start until the code clears?

 

possible VSS (vehicle speed sensor)

 

my 95 c 1500 just started doing the same thing last month! i had a power steering leak, but the issue got worse after fixing the leak...i think the fluid shorted something out?? did you ever get this resolved for you truck??

thanks

 

check your ground to the computer and the ignition something might just be shorting out, possible a wire is just grounding out on something and needs to be adjusted.

 

No you can not tie it to another 12 volt source without switching it!!!!!!!!!