98 F150 light issues

Son’s truck – new engine installed in Feburary, been working fine.  Has a Viper alarm system on truck.  ABS light has been on solid.  Now when truck is started ABS begins flashing.  Replaced 3 blown 15 amp fuses.  Will have to verify which ones, but all light or brake related.  Now I notice all lights in rear of truck stay lit as soon as the headlights are turned on.  This truck also has daytime running lights (DRL).  I am wondering if a ABS sensor is shorted, but don’t see anything running to rear drums even though one fuse I replaced is for rear ABS (RABS)?  I am going to check the stearing column for possible wiring issues, but where do I find the ABS sensors?  Are they front and rear?