sounds like you replaced the EPS controller board
but once again i ask
which fuse did you replace that keeps blowing?

by all means do like edward says, isolate the battery from the truck frame or at least check for shorts to the frame from batt pos and neg. Being that the system is isolated from the frame anyway by design, so ground is actually the neg circuit you don't want any readings to the frame.
If you do read voltage from either side of the battery circuit then you will have to isolate where it is coming from and the first step would be removing the battery away from the frame to eliminate that.

what i'm curious about though is why you had to replace the board in the first place, what fried it? It could be a bad (steering) motor if this is the EPS board you replaced as i suspect.