section 1.401(k)-1(b)(4)(iii)(B) last sentence
Similarly, an employer may not aggregate a plan (within the meaning of section 1.410(b)-7(b) using the ADP safe harbor provision of section 401(k)(12) and another plan using the ADP test of section 401(k)(3).
or if Willy Wonka rewrote the regs about trying to combineg a safe harbor with a non-safe harbor plan
Wonka: [angrily] Wrong, sir! Wrong! Under section 37B of the contract signed by him, it states quite clearly that all offers shall become null and void if - and you can read it for yourself in this photostatic copy - "I, the undersigned, shall forfeit all rights, privileges, and licenses herein and herein contained," et cetera, et cetera... "Fax mentis, incendium gloria cultum," et cetera, et cetera... Memo bis punitor delicatum! It's all there! Black and white, clear as crystal! You have one safe harbor plan and another non-safe harbor plan., so you get... NOTHING combined!!! You lose! GOOD DAY, SIR! [returns to work]