Some common darlington transistors require a higher base voltage to fully "switch on." That might be an issue.

Could be and could be any number of things. Meth in post #4 provided a good example of a transistor driver and while the TS claimed to be using one they provided no schematic or part numbers or even a link to the relay in use? Beats me!

Ron

 

a darlington transistor may be drawn the same as a single transistor sometimes. I favor the MPSA13, although others will also work.