actually it depends on which controller is in this unit
there are traction based controllers and pump based controllers
generally in electric sissorlifts and boomlifts the controller serves a dual role as a traction controller and hydraulic controller. Most of the ones i've seen are the sevcon MOS90 series.

Now looking at the trouble code chart there are 2 possibliities here
Traction controllers:
3 flashes
Bypass contactor welded - recycle through neutral to clear.
Contactor coil short circuit - recycle the key switch to clear.

Pump controllers:
3 flashes
Short circuit across Mosfets, or motor open circuit.

I would check the bypass contactor for welded tips
this may explain why replacing the controller did not fix the problem.

Also remember when replacing a controller you may be required to set it up with the manufacturer's settings, sevcon does not custom set their controllers to anything other than the base settings any controller comes with. Furthermore you WILL need the handset to change any settings in the controller. Yes it might run "as is" but it will not be setup correctly and could damage the controller if you run it that way. As for getting any setup information from grove? good luck with that, grove manlift division went out of business years ago so information is hard to come by these days unless someone(that already has it) feels generous about it. I myself dont have any specific manuals related to this machine so i cant help you there. sorry.