Intermittent Check engine/stop engine light

Hi Guys,

I just bought a 1998 peterbilt 379 EXHD with a 12.7 detroit. It's got an electrical problem that the previous owner couldn't figure out. At higher RPMs it will flash the check engine light and occasionally the stop engine light also. But its just for a brief second then it goes away. I can drive it all day at low rpms with no problem. It seems to throw a random code also. I suspect its a power or ground wire loose somewhere. Also it completely died on me one time with no code, like turning the key off. I suspect that this is a loose wire at the ignition switch. My question is could the ignition switch cause the CEL/SEL. What else could it be?