Check Engine Light not working

How do you know it SHOULD be on?
The engine is not running quite right and I wanted to check the trouble codes. This would be the fastest way to diagnose the problem.

I did test the TPS separately and found it to be faulty. I suppose I could test each sensor, but it would be easier if the check engine light pin was working.

I edited the initial post to add that this is a 94 magnum swapped into my Barracuda.