Do you mean the code tester. Is the check engine light on? If so, you can take the vehicle to any auto parts store and they will run a code check for free.
All you need is a paper clip. Here is a how to guide for a mustang, but the same procedure applies your truck....http://www.mustangandfords.com/how-to/interior-electrical/1510-how- to-manually-test-eec-iv-obd1-trouble-codes-on-a-fox-body-mustang-for-free/
Here is a video...https://www.youtube.com/watch?v=-Nm_J4HHWP8
Looking for a Used F-150 in your area?
CarGurus has 11,298 nationwide F-150 listings starting at $369.
Search Ford F-150 Questions
Ford F-150 Experts
Related Models For Sale
Used Cars For Sale