No lockup??

[The_Dealer]

well i swapped in a 4.0 torque converter in my a4ld and 2.8(low stall). i love the way it turned out, and makes my rig drive so much better. i had a manual t.c. lockup switch wired into the trans. for some reason it wont lock up with the 4.0 converter. everything else is ok. any ideas? trans fluid is in the upper end of the hash marks, and it shifts fine. is it just not a lockup converter? the converter is a pro king from advance from a 92 4.0 ranger a4ld 4wd