4x4 wont engage
 

99 ford 250 super duty - electronic shift on fly switch doesnt work. I checked #17 30amp - it looks good. Looked at relay switches in slots 39 or 40. Cant remember which. They look good - I have no idea how to tell they are bad -4X4 worked once after unplugging relays and fuses - but wont work now after repeating same steps as mentioned above. Any ideas before I start replacing everything. Also, already replaced shift switch.

Thanks for the advice