OK, just added Lezyne E50 and Hecto rear fender lights to a Giant Lafree E+2.
That is these lights:
Like others have said, remove two motor mount bolts and let it pivot on the third bolt:
Then pull down the connectors out of the down tube; this shows two unconnected connectors; a three pin and a two pin rear light connector (JST 02R-JWPF-VSLE-S 2 pin receptacle) with a white (+6V) and a grey (GND) wire:
Note you will have to remove the white rubber cover before connecting to this two pin connector. You will have to draw the wiring further down the down tube to reach the front connector; its near the round handlebar control plug right up at the top shown with my light (yellow and black wires) connected:
After pulling the wires down the down tube for front light, and following the wiring up fender for the rear, then it just remains to terminate the wires grey to GND and white to +6V with a 2 pin JST JWPF plug (02T-JWPF-VSLE-S) using JST SWPT-001T-P025 crimp pins:
Put your bike back together, and now the lights work from the front handlebar switch!
... hope someone finds this useful.