I don’t know if V1 Rambo firmware comes with laser enabled by default(im using SKR pro) but if your sure of your wiring, what have you tested ?
Once connected to your board via USB in a gcode console, does M3 S1 light on the laser ? (M5 to light it off)
Try to look here, not same laser but it talks of 12V laser on Rambo 1.4 so it could help: