Turn the V4 Sign Controller OFF.
Unplug the Radio Link connection (RJ45 connector). Then Plug it back in.  Unplug and plug in 3 times. This helps with cleaning the pins of the connectors.

With the V4 Sign Controller still in the OFF position, slide the Test/Normal switch to Test

Next, turn the V4 Sign Controller ON.  Then slide the Test/Normal switch back to Normal.

The only lights that should be on are the:
RTS
DTR
CTS
+9V

Data light on the front of the V4 Sign Controller should be flash.