it's rare for an ez-a to not do anything, typically its the display unplugged, can you check your connections on the system card? specifically the ones that have screws mounting the plug. the speed encoder can plug into the display port and vice versa, also there is a diagnostic port that these connectors will fit into and create this scenario.

if above is all good, ohm out fuse fu4 (on system card) to the keyswitch wire s2 (at the key), should have continuity. if the fuse was of a higher amperage the potential is there for the system card to have been damaged.
also check key switch wire s1 to terminal strip ts19-5 (mast cable terminal strip) should have continuity.

Thanks for the reply stam, I should have put that in my post. EZ-A-00-16236.

Need serial number to assist with this.
There are a few versions of this truck.