rebuilding a greenforce umbilical torch

Hi,
first post here. im an electrician but not great with electronics and have a few questions regarding a torch/project i bought. basically the greenforce torch doesnt use a switch but a screwcap to make the circuit. the guy who sold it to me bought a new battery which is too short to make contact with the screw cap. so what i want to do is switch it from the torch head with a reed switch. the problem i have is that im switching 12v 50w max which is 4.2A and too much for a reed. I have ordered a MOSFET to take the load.
My question is, can I just use the mosfet and reed direct from the battery or do i need and resistors?? Will the MOSFET disconnect when the mag moves off the reed or will it latch?? or will the lamp remain on? will the MOSFET overheat with 4/5A running through it???
Sorry for all the questions but can ANYBODY help?????:shakehead
Johnny.

:welcome:
Moved to Homemade and Modified Flashlights Discussion - Norm

Get the Taskled Hall or Hall toggle.

BTW, this thread may need to go in dive lighting. Many GF torches modded there.

Thanks for the replies. Any kinks to these switches? i would rather not drill the housing if I can help it, hence, the reed switch.....
any links to the greenforce mods??
Thanks again guys.:wave:
Johnny