88 4runner check engine lite on

[88yooperrunner]

Hi, my check engine lite just came on. Its an 88 with the 3.0 motor, and an auto. In the manual it shows that I can use a jumper wire to check the codes, but I don't see the "box" that I put the jumper wire into???? Any help??? This thing still runs great with 160000 on it!!!! Want to get the problem fixed asap! If possible. Thanx in advance