I know it's a shot in the dark that anyone here as dealt with this, but here goes.

I have a cab I recently picked up (Taito's Double Axle aka Power Wheels) that uses a similar gearshift that's in Chase HQ, SCI, and some other driving cabs, one that has a nitro button on the side of the shifter. The button on mine isn't working and I can't seem to figure out how to get to the insides of the shifter handle to check the microswitch.

Even if I completely disassemble the shifter mech (which o have not done), that still doesn't help with how to separate the two halves of the shifter handle to get to the button.

They have generic aftermarket shifters available but the one on this game is rather unique in that it has the normal up/down for high/low, then it shifts to the right for reverse.