celebrity engine codes

ok i got a 89 chevy celebrity 2.8, i got a check engine light but i dont konw at what spots to stick my little metal thing that suppose to tell me the codes, can any help me ? and also how does the car have to be to check the codes, i mean does it have to be warm, does the key ahve to eky on, the car runnin ?

plz help

Short the two connectors on the top right corner of the data terminal plug, this grounds the diagnostic terminal and will flash the code on the 'Service Engine Soon' light. The ignition key must be on and the engine stopped.