Looking at the 7i76 manual, the speed control looks the same as the 7i78. My vfd an NF-9000 puts 10v+ve on the terminal marked 10v, and 0v on ACOM. I would check the volts on those connections.
On the vfd I connect FWD to DCOM for forward, and REV to DCOM for reverse. I would start by getting forward/reverse working with the correct terminals for your vfd ie just use a switch, (take care not to short anything out). When you have this working, you can look into whats needed from the 7i76. (I spent several hours trying to find a fault on the vfd, when the problem was an intermittent fault on one of the relays)
Either you go with enable and direction signals or with forward and reverse signals.
Have a look with of the two ways is presented at your mesa output pins. Than connect the two to your vfd. At last change with P parameter the behaviour of these two vfd input pins. Done
The motion component has a motion.spindle-forward pin, and a motion.spindle-reverse pin. Run your config. Do Machine, Show Hal Configuration, then watch those pins while you select spindle forward/reverse in manual control. If they come on, they just need mapping to the appropriate output. There is also a motion spindle on pin, mine comes on for forward or reverse.
