where is the block to hook up jumpers to read codes manually?

[crank182]

I want to manually read the codes in my computer, its a 93 s10 blazer 4.3L z code 2wd 5speed, i read you can manually read the computer codes by hooking a jumper wire to the a and b terminals in the test block, the book says it's under the dash on the passenger side but it's not there, the only thing there is the computer. I read you jump with the ignition off, then turn it to run, the check engine light will blink 3 times the in a succession of blinks to indicate stored codes with a pause in between, sounds simple and i have a list of all the codes the blink will indicate but can't find where to put the jumper, anyone know where its at on my truck? thanks for looking.

[Jeremy-WI]

usually under the dash on the drivers side