Help with IRF1405 MOSFETS

So,

I brought 6 IRF1405 MOSFETs (is.gd/iqx3W - Datasheet) and when I connect it up to my arduino and then my christmas lights they stay on - no matter if I'm putting the gates pin high or not. In the datasheet it says that the Vgs(th) is 2-4V but the Vds = 20v.

I'm wondering if I do need to get the gate pin up to 20V or not. If so, I brought the wrong MOSFET and I'm wondering if you had any ideas controling 32v 1a christmas lights using a 5v gate.

Thanks, Matt

How do you have them connected? N-MOSFETS should be used as low-side switches, between the load and “Gnd” rather than between the power and the load. And you need to have a common GND connection, of course…

A logic level mosfet would be a better choice.

Lefty