Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP)
Flight Crew Total 6
Fatigue; Distraction
Deviation / Discrepancy - Procedural Clearance; Ground Incursion Taxiway
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification
Airport; Environment - Non Weather Related; Human Factors
Night landing in MMGL; my first trip into MMGL; end of a long 4 leg day; including an aircraft swap on the second leg after we preflighted it; causing us to be delayed all day.  After landing Runway 28; we were given  clearance to taxi to the gate via A and D; cross Runway 02; contact Ramp entering D.  Captain was taxiing; I  was heads down completing the After Landing checklist.  He asked if this was D; I looked up and  couldn't quite read the sign; which was obstructed by tall grass and dark.  At the last minute; I made out  a 'D' and said yes; turned out I was mistaken; it indicated D was the next taxiway.  After he made the  left turn; we saw F painted on the pavement.  He stopped the aircraft and I advised Ramp we had  entered at F instead of D.  Even though our path to the right was clear; Ramp did not allow us to turn  right toward our gate from F; but instructed us to taxi to the left out G; hold short of A and contact  Ground.  There were no light aircraft in the ramp area blocking our path; and after clearance from  Ground we proceeded back down A to D without incident. Suggest encouraging MMGL to trim grass around taxiway signage; and ensure signage is clearly lit and  visible at night.  Suggest encouraging crews who are unfamiliar or lack recent experience to a field to  suspend/delay checklists well prior to upcoming turns; and ensure both pilots are heads-up to provide a  positive cross-check of taxi route.
Air carrier First Officer reports entering the ramp at MMGL on the wrong taxiway due to tall grass obscuring a sign and night time conditions.