New user here, so excuse me if this is the wrong category.
I have a tachometer from a car that I want to control using my Arduino UNO. The tachometer is an old-style air core gauge, with three pins: Ground, 12V and a signal pin that seems to take square wave 12V input.
I've been able to control the tachometer using a mechanical relay that turns on/off 12V to the signal pin. But because of its mechanical nature I hit the limit at about 3000rpm on the gauge, and then the relay won't go any faster. So I need something quicker, and I got my hands on an IRF630 N-channel transistor, but my Arduino doesn't seem to be able to turn it completely on - the transistor will only let through ~2V when I send 5V to the gate - if that's the Arduino or the transistor I don't know, but it "opens" fully when I apply 12v to the gate.
This may be a XY problem, but I could need your advice on what transistor would be a nice fit for this project?