i understand from what you explained that you should give 12v to your lock and there is another sepearte input to trigger it to open. when you power it on by 12V transformer at the same time you give input to open (trigger), this may be the reason why it doesnt response.
1st do the following checks.
energize it by 12V and seperately trigger it by the specific pulse input,
if it works, then you should wire it to get 12v permenantly and the trigger input only when the gate arms get the signal.
use a 110V relay as a switch for this trigger input, no matter it last for 2min.
if you want to just switch it on for few second and relase it then use a specific relay to give the time delay.