I've just looked at battery and it's a 70A battery so should be ok there, but perhaps as per you suggestion to putting an amp meter inline and monitoring the steering whilst driving rather than static may show something, if it is an overload issue the draw is either of short duration or lowish as the 40A fuse has not popped yet, I have a pico setup so can log the draw that.
As for speed signal, I have a module attached which produces two square waves, one at 82Hz, this feeds into the EPAS on Pin 15 and represents the engine running, the second signal is variable via a pot and is between 19Hz and 295Hz and feeds into Pin 7 of the EPAS and represents MPH, this pot allows for adjustment of assistance to the steering. I have also wired in a warning lamp as would be in the dash of the donor car but as yet have not seen this lit when fault occurs. Perhaps someone can confirm that the warning light is lit at ignition on position and goes out once started, I believe as the pulse generator I have attached to my EPAS start's as soon as ignition is on it doesn't have a reason to light my warning lamp.
Thank you for the feed back you guys are giving me.