I picked up a 1997 Ford Explorer Sport at an auction. Everything is fine except the Check Engine Light wont come on causing it to fail SMOG test. I replaced the fuses, changed the bulbs in the Instrument Cluster, checked connection from the cluster back to the MIL and even replaced the Instrument Cluster with a known working one. Any suggestions?

 

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Replacement bulb was ohm/cont checked? Have to ask
So,, since the cluster/board was replaced, bulbs are new, one of a few things is going on. It could be that the grounding wire to the PCM was purposefully cut to cancel the light, or, there’s a drop out at the cluster connector itself, or on down to the PCM connector, or, the PCM no longer is suppling the ground to illuminate the lamp.

Power distribution to the CEL on the printed board is shared, and the ground is supplied by the PCM for activation.
On the PCM connector, the ground for the CEL is on pin #2 I believe. S/B a PK/LG wire. You can ohm test between the disconnected PCM to the cluster connector to check for continuity. If there, reconnect and apply a ground test at the PCM. If the CEL illuminates, PCM has lost its grounding function...