jumper wire/scantool

[rezsst]

in my repair manual it says i can use a jumper wire to read codes. when i do this the fans come on and no cel. i cant get the codes. if i trace the wires back to the pcm can i use the jumper wires from there. if so can someone tell me where the wires go into the pcm. this would save me the time of tracing the wires. there is 4 plugs that goes into the pcm labled red,blue,black,and the last one was green. not sure on the last color.if the jumper wire dosen't work will a scan tool work? its a 94 caprice classic wagon 5.7 please respond. thanks