Cannot retrieve mil codes light stays on?

Just to be sure you are getting the correct pins, here is a guide that will help with this.

https://www.2carpros.com/articles/toyota-trouble-code-definitions-and-code-gathering-method-1990-1995

If you are not getting any codes, then that normally means the ECM has failed and is no longer communicating. The vehicle may still start and run but a check engine light with no codes is showing that the ECM is the issue.

I am attaching the process below on how to replace this as I suspect that is what is going to have to happen. However, if you get some codes, let us know what they are, and we can go from there.

Thanks