Here - this picture might help?....
Did you cut the board in the YELLOW circled area or in the RED circle?
- It does look like some circuit board traces do run under the Yellow area - so inspect there carefully. They might be able to be repaired using some fine strands of wiring to bridge them over?
Another test you could run before removing the control unit from the HL - do the emergency stop hazard lights work? If they don't -- I'd be scratchin' my head a bit, since that circuit isn't part of the repair you did (just something else to try)...