Audio Research VT100 MKll Stays on

I've replaced the switch twice which both times worked for a while and then the same thing
Terrybbagit

Replaced the switch twice?
Replaced the switch twice in the ARC VT100 or in the power conditioner?

If you mean the switch in the power conditioner you should be using the power switch on the ARC VT100 to turn the amp on and off. The amp may have circuitry that limits start up inrush high current incorporated in the amp's on/ off switch circuitry. Check with ARC.

Also should mention the power switch on the ARC is a snap switch and should be operated in a fast action motion whether turned on or off. The faster the action the better to help limit arcing of the contacts, especially on turn off. Excessive arcing will burn up the contacts and the switch will fail prematurely. In some cases the contacts can/will arc welding the contacts together. In this case operating the switch handle will not open the contacts breaking the circuit.

Are you using the 12v trigger in the back? If so, that's probably causing the problem.

It is the switch on the amplifier that I replaced and its not plugged in to a 12v trigger just the switched outlet on the conditioner as I said with the switch completely removed and plugged into a different outlet I still have power I have also check the switch with an ohm meter and it tested fine so I know it has nothing to do with the switch
Thank You

If that's not switch than there must be capacitor-relay issue.
The capacitor-relay is usually implemented to prevent from shock. The switch connects to low-voltage circuit that engages the high voltage circuit.
Plugging and un-plugging your amp is much better solution than keeping it on all the time.

Contact ARC service.
Just guessing, the manual on/off switch must operate a power on/off relay being held closed electrically by the coil being energized for some reason, or the contacts of the relay are arc welded closed.